Easy to Build Plans and Instructions

How To Use Measuring

and Layout Tools

In this book, you will learn about different types of measuring and layout tools and and how to use them. You will also learn how to select the right measuring and layout tools for your do-it-yourself project, read various types of measuring tools, and provide the proper care of measuring and layout tools to keep them in good working condition.

How To Read The Scale of a Ruler or Tape Measure

In one sense, the term "scale" means the scale of a drawing. In another sense, it means the succession of graduations on any graduated standard of linear measurement, such as the graduations on a steel tape or ruler.

The more common type rules and tapes are divided into fractions, inches, and feet. Explained here are the scales on a 12-inch steel machinists rule (Figure 1).

Picture of a 12 inch steel machinist's rule
Figure 1 - 12-inch Machinists rule.

The rule is divided into twelve inches. The inches are further divided into eighths, sixteenths, thirty-seconds, and sixty-fourths.

Look at the rule. There is a small numeral marked on the end of the rule nearest the 1-inch mark. This numeral indicates the number of divisions per inch (Figure 2).

Picture of a section of a steel ruler showing divisions per inch
Figure 2 - Divisions per inch

When referring to fractions, always use the reduced name. This is the smallest numerator (top number) and denominator (bottom number). For example, 3/6 can be reduced to 1/2 by dividing both the top and bottom by 3. Generally, fractions may be reduced to their lowest forms by repeated division by 2 or 3.

Look at the section between the "2" and the "3" on the edge marked with an "8" for eighths (Figure 3).

Picture of a ruler section showing an 1/8 inch divisions
Figure 3 - 1/8 -inch scale

There are eight equally spaced lines. The lengths of these lines differ and indicate different fractions or parts of an inch.

The longest line is in the center and is equal to 4/8 - or 1/2-inch. Each half-inch is divided in half by a slightly shorter line indicating 2/8- or 1/4-inch on the left and 6/8 - or 3/4- inch on the right.

Each 1/4 -inch is divided in half by the shortest line which indicates 1/8 -inch, and will indicate 1/8 -, 3/8 -, 5/8- and 7/8 -inch.

Now turn the rule and look at the edge with a 16 marked on it (Figure 4).

Picture of a ruler section showing an 1/16 inch divisions
Figure 4 - 1/16-inch scale.

There are now 16 equal divisions between each inch. Since 2/16-inch reduces to 1/8 -inch, divide each 1/8-inch into two equal parts producing 1/16-, 3/16-, 5/16-, 7/16-, 9/16-, 11/16-, 13/16-, and 15/16-inch.

Common tapes and rules usually are not graduated smaller than sixteenths. However, precision measurements require smaller graduations.

Look at the back of the machinists rule. Find the edge marked 32 (Figure 5) and once again look between the numbers "2" and "3."

Ruler showing 1/32 inch divisions
Figure 5 - 1/32-inch scale.

To read this rule, remember:

1. Sixteen divisions (16/32) are equal to 1/2-inch.

2. Eight divisions (8/32) are equal to 1/4-inch.

3. Four divisions (4/32) are equal to 1/8-inch.

4. Two divisions (2/32) are equal to 1/16-inch.

To read 2 5/8-inches on the scale, first find the two inch mark, then determine the number of 32nds in 5/8-inch.

To determine the number of 32nds in 5/8-inch, remember four divisions or 4/32 are equal to 1/8-inch. If 1/8-inch is equal to 4/32-inch, then 5/8-inch is equal to 20/32-inch as shown:

If 1/8 = 4/32, then 5/8 = 20/32-inch (4 x 5 = 20)

1. Find the 20/32-inch reading on the scale as shown above.

2. Write the new fraction 2 20/32-inches.

Finally, look at the edge marked 64 (Figure 6). Each inch is now divided into 64 equal parts.

Picture of a ruler section showing an 1/64 inch divisions
Figure 6 - 1/64-inch scale.

To read this rule, remember:

1. Thirty-two divisions (32/64) are equal to 1/2- inch.

2. Sixteen divisions (16/64) are equal to 1/4-inch.

3. Eight divisions (8/64) are equal to 1/8-inch.

4. Four divisions (4/64) are equal to 1/16-inch.

5. Two divisions (2/64) are equal to 1/32-inch.

To read 2 3/4 -inches on this scale, first find the two inch mark. Next, determine the number of 64ths in 3/4 -inch.

To determine the number of 64ths in 3/4 -inch, remember every sixteen divisions or 16/64 are equal to 1/4-inch. If 1/4-inch is equal to 16/64-inch, then 3/4-inch is equal to 48/64-inch as shown:

If 1/4 = 16/64, then 3/4 = 48/64-inch (16x3=48)

1. Locate the number 48 between the 2- and 3- inch marks on the scale.

2. Write the new fraction 2 48/64-inches.

How to Read a Metric Ruler

The metric system is based upon multiples of ten. For example, there are 10 millimeters in a centimeter and 100 centimeters in a meter.

Picture of a Metric ruler
Figure 7 - Metric rule.

The example provided will deal only with millimeters (mm).

The meter is the starting point. From that point, there are two scales for measuring. A meter divided by 100 equals a centimeter (cm), 1/100 or 0.01 meter.

Next divide a centimeter (cm) by 10. This will equal a millimeter (mm), 1/1000 or 0.001 meter.

Now let's look at a section of the rule between 2 cm and 3 cm.

There are 10 equal divisions which are equal to 1/10 cm or 1 mm.

To measure 26 mm, first locate the longest line designated 2 cm or 20 mm.

Next count 6 additional lines to find 26 mm.

There is a table for converting from U.S. Common to metric or vice versa in the inside back cover of this manual.

Measuring and Layout Tools

There are many types of tools used to measure and lay out projects. Measuring tools include flat steel rules, measuring tapes, wooden folding rules, digital measuring devices, and measuring wheels. Levels are used to check that project components are level and/or plumb. Plumb bobs are used to check that project components are perfectly upright. Squares are used to mark, check, and measure components of construction projects. When you consider which of these tools to use, keep in mind the following points:
 
  • The tool must be accurate.
  • The tool should be easy to use.
  • The tool should be durable.
  • Numbers on the tool must be easy to read. Black numbers on a yellow or off white background work well.

Rules and Steel Tapes

The rule or tape is used for measuring where accuracy is not an extremely critical factor. They can be rigid or flexible, come in various lengths, and can be made of wood, metal, cloth, or fiberglass.

Flat Rules

The flat steel rule (Figure 8) is the simplest measuring tool. It is usually 6 or 12 inches in length but can be longer. Steel rules can be rigid or flexible, thin or wide. It is easier and more accurate to use a thin rule, since it is closer to the work being measured.

Picture of a 12 inch steel ruler
Figure 8 - Steel rule.

Flat steel rules can have up to four sets of marks, two on each side of the blade. Rules with four sets of marks are set up with divisions of 1/8 inch and 1/16 inch on one side, and divisions of 1/32 inch and 1/64 inch on the other side. The marks are longer for a division of 1/2 inch, scaling down in length from 1/4 inch through 1/64 inch.

There are many variations of the common rule. Sometimes the graduations are on one side only, sometimes a set of graduations is added across one end for measuring in narrow spaces, and sometimes only the first inch is divided into sixty-fourths, with the remaining inches divided into thirty-seconds and sixteenths. A metal or wood folding rule may be used.

Folding Rules

A folding rule (Figure 9) is made up of hardwood, steel, or aluminum sections, each measuring 6 to 8 inch. The sections are connected by spring joints that unfold for measuring distances.

Illustration of a partially folded folding ruler
Figure 9 - Folding rule.

These folding rules are usually from 2 to 6 feet long. The folding rules cannot be relied on for extremely accurate measurements because a certain amount of play develops at the joints after continued use.

Measuring Tapes

A measuring tape (Figure 10) can come in any length from 6 to 50 feet. The most common are 10, 16, and 25 feet. Shorter tapes usually have a curved cross section so they roll easily but stay rigid when extended. Longer tapes are usually flat and should be laid along a surface to avoid sagging in the middle.

Measuring tape.
Figure 10 -Measuring tape.

A locking mechanism, such as a sliding button, keeps the tape locked in place while a measurement is being taken. Other locking mechanisms, such as levers and toggles, allow the tape to be retracted after measuring by simply squeezing them. In any case, a spring mechanism in the case automatically retracts the tape.

How to Use a Measuring Tape

Follow these steps to use a measuring tape properly:

1. Pull the tape out to the desired length.

2. Place the hook over the edge of the material you are measuring.

3. Lock the tape in place.

4. Record or mark the measurement.

5. Unhook the tape from the edge of the material.

6. Release the lock and rewind the tape.

Digital Measuring Devices

Digital measuring devices (Figure 11) are similar to conventional measuring devices, but their digital readouts make measurement readings more precise. They give you the ability to convert fractions to decimal or metric equivalents. A useful function of these devices is their ability to compensate for the size of the tape case when making measurements inside a window frame or door jamb. Some devices have a memory function that holds a measurement; others have a voice recorder to keep track of multiple measurements.

Illustration of a digital tape measure showing the steel tape and the corresponding digital  dispay

Figure 11 - Digital measuring device.

SQUARES

Carpenter's Square

The carpenter square (Figure 12), has a large arm, called the blade, and a small arm, called the tongue. The arms meet in a 90-degree angle. The square is used to mark, check, and measure components of construction projects. It has several scales etched onto the surface for quick reference: a diagonal scale, a board foot scale, and an octagonal scale. It has ruler increments etched on the inside and outside edges.
Picture of a steel Carpenter's square.
Figure 12 - Carpenter's square.

The face side contains the manufacturer's name and the inches are divided into eighths and sixteenths (Figure 13). There are two tables down the center.

Illustration showing the parts of a carpenter's square, inluding the face, tongue, blade, body, and scale.
Figure 13 - Parts of a Carpenter's square.

The rafter table is used for determining the length and cut of rafters.

The octagon or eight square scale is used for cutting an octagon from a square piece of material.

The back side contains the hundredths scale and is divided into tenths, twelfths, and sixteenths as shown. There are two tables down the center.

The Essex board measure is used to compute the number of board feet in a given piece of lumber.

The brace measure is used to find the exact lengths of common braces.

Common scales or inch divisions found on the carpenter's square are listed in Table 4-2.

Table of scales and measurements of a Carpenter's square
Table 1 - Scales and measurements of a carpenter's square

Try Square

The try square (Figure 14) is an L-shaped tool used as a guide to lay out 90 degree cuts with pencil markings. It is also used to check that the edges and ends of boards are square, and whether a board is the same depth along its entire length. A try square has broad blades 6 to 12 inches long set at right angles.

Illustration of a Try sqaure used as a marking and cutting guide.
Figure 14 - Try square.

Combination Square

The combination square (Figure 15 ) is used for many purposes in woodworking and metalworking but mainly for measuring the accuracy of a right angle. It is made up of the following components:

1. A slotted 12-inch stainless steel rule which is graduated in eighths, sixteenths, thirty-seconds, and sixty-fourths of an inch. It can be used as a measuring scale by itself or with any one of the following components.

2. The center head, when attached to the rule, bisects a 90-degree angle. It is used for determining the center of cylindrical work.

3. The protractor has a level and a revolving turret which is graduated in degrees from 0 to 180 or 0 to 90 in either direction. It is used to lay out and measure angles to within 1 degree.

4. The square head has a level, a scribe, and 45- and 90-degree sides. It is used to lay out 45- and 90-degree angles and to check level. It may also be used as a height or depth gauge.

Picture of Combination square detailing the steel rule, center head, protractor, level, revolving turrent, 45 degree and 90 degree sides, square head and scribe
Figure 15 - Combination square.

Sliding T-Bevel

The sliding T-Bevel (Figure 16) is made up of a slotted blade and a solid stock. The blade is adjustable so it can be set to measure any angle. The T-Bevel is used for testing bevels and laying out angles.

Picture of an open sliding T-bevel showing the slotted blade and solid stock
Figure 16 - Sliding T-Bevel.

Bevel Protractor

The bevel protractor (Figure 17) is made up of an adjustable blade and a graduated dial which contains a Vernier scale. The bevel protractor is used to establish an angle and determine its relationship to other surfaces. The acute angle attachment is used for measuring acute angles accurately.

Picture of a Bevel protractor showing the adjustable balde and graduated dial
Figure 17 - Bevel protractor.

Rafter Angle (Speed) Square

The rafter angle square or speed square (Figure 18) is a three-sided, triangle shaped measuring tool. It is used to draw perpendicular lines on boards to be cut, or to lay out angles for rafters, stairs, and other construction projects. It has degree gradations etched onto the surface for quick layout and cutting of lumber so you don't have to perform angle calculations.

Picture of an aluminum rafter angle square, or speed sqare.
Figure 18 - Rafter angle square.

T-Square

The T-Square (Figure 19) is used to measure and cut drywall. Some table saws come with a T-Square fence attached.
Picture of and aluminum T-square.

Figure 19 - T-Square.

How to Use a Carpenter's Square to Mark a Square Line

To mark a line for cutting, use the following steps:

1. Find and mark where the line will be drawn.

2. Line the square up with the bottom of the object to be marked as shown in Figure 20.

3. Mark the line to be cut; mark an x on the material to be cut away.

4. Cut off the excess material.

Picture showing how to use a Carpenter's square to mark a square line

Figure 20 - Using a carpenter's square.

How to Check for Square

Check that joints meet at a 90-degree angle by placing the blades of the framing square along the two sides of the angle, as shown in Figure 21. If both blades fit tightly, the material is square. If there is any space between either of the arms and the side closest to it, the material is not square.

Picture showing how to check for square

Figure 4-21 - Checking for square.

How To Use a Carpenter's Square to Layout Steps

1. An example to properly position a square when marking cut lines for a series of steps 9 inches by 12 inches is illustrated in Figure 22.

2. Continue the process until desired number of steps has been laid out.

Illustration show how to use a Carpenter's sqaure to layout steps on a stair plate.
Figure 22 - Square position for steps

How To Use a Try Square

Using a try square (Figure 14) is similar to using the carpenter's square.

1. To check a square joint, place the stock against a horizontal section and the blade against a vertical section. Light must not be seen around blade edge. If light is seen, the work is not square.

2. To check the end of a board, place stock on vertical edge and extend blade over the end. Light must not be seen around blade edge. If light is seen, the work is not square.

How To Use a Sliding T-Bevel Square

Follow these steps to use a sliding T-Bevel properly:

1. Loosen the locking nut and adjust blade to measure a desired angle using a protractor (Figure 23). Tighten the locking nut.

Illustration showing how to use a sliding T-bevel using the protractor, blade and locking nut
Figure 23 - Set the sliding T-Bevel.

2. The angle may now be laid out by extending the blade across the board with the stock (Figure 24) held firmly against the edge.

Illustration showing how to transfer and angle using the T-bevel square

Figure 24 - Transfer the angle to the material.

3. Mark with a pencil or marking crayon. Make sure the square does not move while marking (Figure 25).

Illustration showing how to mark an angle with the sliding T-bevel square.

Figure 25 - Mark the angle.

How To Use a Combination Square

Follow these steps to use a combination square properly:

Using as a Center Head to Find the Diameter of a Cylinder

1. Slide center head on rule and fasten by tightening setscrew (Figure 26).

Illustration showing how to set the center head on a combination square

Figure 26 - Set the combination square.

2. Put the center head flush against the cylinder (Figure 27).

Illustration showing how to use  a combination square center head to find the diameter of a cylinder

Figure 27 - Press against the cylinder.

3. Mark the diameter on the cylinder (Figure 28) using a pencil or marking crayon by drawing a straight line along the inside edge. Make sure the square does not slip while marking.

Illustration showing how to mark the diameter of a cylinder with a combination square.

Figure 28 - Mark the diameter.

Using as a Protractor Head to Determine an Angle

1. Slide protractor head on rule (Figure 29) and fasten by tightening set screw.

Illustration showing how set up the protractor head on a combination square

Figure 29 - Set up the combination square.

2. Loosen the protractor adjustment screws so the protractor may be pivoted about the rule. Angle being measured is already marked.

3. Place the rule on the angle being measured (Figure 30) and pivot the protractor head against the edge. Tighten adjustment screws.
 
 

Illustration show how to measure an angle using a combination square with the protractor head installed

Figure 30 - Measure the angle.

4. Remove and read the measured angle on the protractor scale (Figure 31).

Illustration showing how to verify a angle on a combination square

Figure 31 - Verify the angle.

Using a Combination Square to Mark 90-Degree and 45-Degree Angles

Mark a 90-degree angle (Figure 32) using the following steps.

Picture showing how to mark a 90-degree cut with a combination square.

Figure 32 - Mark a 90-degree cut with a combination square.

1. Set the blade at 90 degrees (a right angle).

2. Place the square so the head fits snugly against the edge of the material to be marked.

3. Use the blade as a straightedge to guide the mark, starting at the edge of the material.

Mark a 45-degree angle (Figure 33) using the following steps.

Picture showing how to mark a 45-degree cut with a combination square.

Figure 33 - Mark a 45-degree cut with a combination square.

1. Set the blade at a 45-degree angle.

2. Place the square so the head fits snugly against the edge of the material to be marked.

3. Use the blade as a straightedge to guide the mark, starting at the edge of the material.

Care of Squares

Observe the following guidelines when working with squares:
  • Wear gloves. The edges can be very sharp.
  • When you use a square as a saw guide, use a clamp to hold the square so you can keep both hands on the saw.
  • Make sure squares are kept clean.
  • Keep the square dry to prevent rust.
  • Use a light coat of oil on the blade. Occasionally clean the blade's grooves and the set screw (if there is one).
  • A square with a loose stock is no good. Replace the
  • square.
  • Use squares for the appropriate purpose and in the correct way.
Avoid the following to preserve the integrity of the square, as they are expensive to replace:
  • Dropping it.
  • Prying or hammering with it.
  • Striking it hard enough to change the angle between the blade and the head.
  • Bending it

Dividers

Dividers are instruments used for measuring distances between two points, transferring or comparing measurements directly from a rule, or for scribing an arc, radius, or circle.

Spring Divider

A spring divider (Figure 34) consists of two sharp points at the end of straight legs, held apart by a spring and adjusted by means of a screw and nut. The spring divider is available in sizes from 3 to 10 inches in length.

Picture of a spring divider showing the points, spring and adjustment screw
Figure 34 - Spring divider.

Wing Divider

A wing-type divider (Figure 35) has a steel bar that separates the legs, a lock nut for setting a rough measurement, and an adjustment screw for fine adjustments. The wing-type divider is available in 6, 8, and 12-inch lengths. Also available is a divider with one removable leg, so that a pencil may be inserted.

Picture of two wing dividers each showing their two legs: one with the point installed and and one with apoint removed and a pencil installed, the lock nut and adjustment screw
Figure 35 - Wing divider.

How To Use a Divider to Scribe a Circle

1. Set the desired radius on the dividers using the appropriate graduations on a rule (Figure 36, Panel A and B).

2. Place the point of one of the divider legs on the point to be used as the center (Figure 36, Panel C and D).

3. Lean the dividers in the direction of movement and scribe the circle by revolving the dividers. (Figure 36, Panel E and F).

Illustration showing how to use a divider to scribe a circle.
Figure 36 - Using a divider to scribe a circle.

How To Care for Dividers

Observe the following guidelines when working with dividers:
 
  • Keep dividers clean and dry.
  • Protect the points against damage.
  • Store dividers where they will not become bent or broken.

Marking Gauges

Marking gauges are made of steel (Figure 37) or wood (Figure 38). They consist of a graduated beam about 8 inches long on which a head slides. The head can be fastened at any point on the beam with a thumbscrew. The thumbscrew presses a brass shoe tightly against the beam and locks it firmly in position. A steel pin or spur marks the wood and projects from the beam about 1/16 inch. A marking gauge is used to mark off guidelines parallel to an edge, end, or surface of a piece of wood. It has a sharp spur or pin that does the marking. A marking gauge must be adjusted by setting the head the desired distance from the spur.

Picture of a steel marking gauge showing the pin, head and locking screw.
Figure 37 - Steel Marking gauge.

How To Use Marking Gauges

Press the head firmly against the edge of the work to be marked (Figure 38). With a wrist motion, tip the gauge forward until the spur touches the work. Push the gauge along the edge to mark the work, keeping the head firmly against the work.

Illustration showing how to use a marking gauge to transfer a dimension to the work piece

Figure 38 - Using a marking gauge.

Adjustable Parallel

Adjustable parallels (39) consist of two tapered parts fitted together. The distance between the two outside parallel surfaces varies by moving mating parts together or apart. This distance is then measured with a micrometer. Adjustable parallels are used as gauges for leveling and setup work. Various sizes are available depending on the nature of work.

Picture of an adjustable parallel for leveling and setup work
Figure 39 - Adjustable parallel.

Levels

Levels (Figure 40) are tools designed to prove whether a plane or surface is in the true vertical or true horizontal. All levels consist of a liquid-filled glass tube or tubes supported in a frame.

Illustration of a level showing the hanging hook, bubble and glass vials
Figure 40 - Parts of a level.

Master Precision Level

The master precision level (Figure 41) has a ground and graduated main vial. The top and bottom of the level are milled and ground to make sure both surfaces are absolutely parallel. This level is used to determine the true horizontal with the main vial. The true vertical is determined by using the two smaller vials.

Picture of a Master precision level showing the main vial and smaller vials
Figure 41 - Master precision level.

Machinist's Level

The machinists level (Figure 42) has an extra large vial, increasing the accuracy and sensitivity. Some of these levels have grooved bottoms which fit over pipes and shafts. They are used in machine shops for leveling work and equipment.

Picture of a small amd large machinist's level
Figure 42 - Machinist's level.

Iron Bench Level

The iron bench level (Figure 43) is made of a special design casting which ensures its lightness, strength, and rigidity. It is used mostly in the construction industry. It may also be used in a machine shop.

Picture of an Iron bench level with extra large vial
Figure 43 - Iron bench level.

Striding Level

The striding level (Figure 44) is a machinists level which is mounted on a raised base. This level is used to span existing cabling, piping, or similar obstructions. It is extremely useful in a machine shop for checking the true horizontal of the flatway on a lathe.

Picture of a Striding Level showing its raised platform
Figure 44 - Striding level

Carpenter's Level

The carpenter's level (Figure 45) has three vials which are mounted horizontally, vertically, and at a 45-degree angle. The carpenter's level is used in construction for checking for true vertical, true horizontal, and 45-degree angles.

Illustration of a Carpenter's Level
Figure 45 - Carpenter's level.

Line Level

The line level (Figure 46) is a single vial in a metal case with a hook on each end for hanging on a cord. It is used to check whether two points are level, such as two points on a floor or in an elevation. It must be used with a tightly stretched cord.

Picture of a Line level for use on a stretched cord
Figure 46 - Line level.

Torpedo Level

The torpedo level (Figure 47) is a small level, generally 6 to 9 inches in length. Its name is derived from its boat-like shape, tapered at both ends. It is useful in small spaces where a larger level would not fit.

Picture of a Torpedo level for use in small spaces
Figure 47 - Torpedo level.

Digital Level

The digital level (Figure 48) has two vials; one to check for level, the other to check for plumb. It also includes a digital readout for:
  • Degrees of slope.
  • Inches per foot of rise and run for stairs and roofs.
  • Percentage of slope for drainage on decks and masonry.


Illustration of a digital level with display showing degrees of slope
Figure 48 - Digital level.

Laser Level

A laser level is used to level and provide reference lines for tasks such as setting foundation levels, establishing drainage slopes, aligning plumbing and electrical lines, and setting tile. It can be mounted on a tripod, fixed to pipes or framing studs, or suspended from ceiling framing.

How Check a Level For Accuracy

A level may be checked for accuracy by placing it on a known level surface and noting the position of the bubble. Reverse the level end for end. Observe the position of the bubble. If the relative position of the bubble was the same for both readings, the level is accurate.

How To Use a Level

The carpenter and torpedo levels are easy to use. All you need is a careful eye to read it correctly.

1. Place the level on the object you need to check. Lay it on a horizontal surface or hold it against a vertical surface.

2. Check the air bubble in the vial. When the bubble is centered between the two lines on the vial, the object you are checking is level if you are checking a horizontal surface, plumb if you are checking a vertical surface, or at a 45-degree angle if you are checking the angle.

Care of Levels

You are not likely to have any personal injuries from using a level. However, you can damage this sensitive instrument if you don't handle it carefully. Observe the following guidelines when working with levels:
  • Replace the level if any of the vials are cracked or broken.
  • Keep the level clean and dry. Keep the level in its case when not in use.
  • Use the level properly. Avoid bending or applying excessive pressure on the level and dropping or bumping the level.

CALIPERS

Simple calipers (Figure 49) are used in conjunction with a scale or rule to determine the thickness or the diameter of a surface, or the distance between surfaces. A caliper is usually used in one of two ways. Either the caliper is set to the dimension of the work and the dimension transferred to a scale, or the caliper is set on a scale and the work machined until it checks with the dimension setup on the caliper.

Illustration showing various examples of outside and inside calipers
Figure 49 - Simple calipers.

How to Adjust Inside and Outside Calipers

To adjust a caliper to a scale dimension, hold one leg of the caliper firmly against one end of the scale and adjust the other leg to the desired dimension. To adjust a caliper to the work, open the legs wider than the work and then bring them down to the work.

Outside calipers for measuring outside diameters are bow-legged; those used for inside diameters have straight legs with the feet turned outward. Calipers are adjusted by pulling or pushing the legs to open or close them. Fine adjustment is made by tapping one leg lightly on a hard surface to close them, or by turning them upside down and tapping on the joint end to open them.

Simple Calipers

The simple outside calipers are bowlegged. Those used for inside diameters have straight legs with feet turned outward. Calipers are adjusted by pulling or pushing the legs to open or close them.

Transfer Calipers

Transfer calipers are used for measuring chamfered grooves or flanges. A screw attaches a small auxiliary leaf to one of the legs.

The measurement is made as with ordinary calipers. The leaf is locked to the leg. The legs may be opened or closed as needed to clear the obstruction. The legs are then brought back and locked to the leaf, restoring them to the original setting.

Hermaphrodite Calipers

Another type of caliper is the hermaphrodite, sometimes called the odd-leg caliper. This caliper has one straight leg ending in a sharp point, sometimes removable, and one bow leg. The hermaphrodite caliper is used chiefly for locating the center of a shaft, or for locating a shoulder.

Spring Joint Calipers

Spring joint calipers have the legs joined by a strong spring hinge and linked together by a screw and adjusting nut. For measuring chamfered cavities (grooves) or for use over flanges, transfer calipers are available. They are equipped with a small auxiliary leaf attached to one of the legs by a screw. The measurement is made as with ordinary calipers; then the leaf is locked to the leg. The legs may then be opened or closed as needed to clear the obstruction, and brought back and locked to the leaf again, thus restoring them to the original setting.

Slide Calipers

Slide calipers (Figure 50) can be used for measuring outside and inside dimensions. Graduations are in inches, fractions, or millimeters. One side of the caliper is used to measure outside and the other side is used to measure inside dimensions. Stamped on the frame are the words "IN" and "OUT." You use them when taking inside and outside measurements. The other side of the caliper is used as a straight measuring rule.

Picture showing a Slide caliper for making inside and outside measurements
Figure 50 - Slide caliper.

Trammels

The trammel (Figure 51) measures distances beyond the range of calipers. The instrument consists of a rule, rod, or beam to which trams are clamped. The trams carry chucks. The trammel can also be used as a divider by changing the points.

Picture of a Trammel showing the rules, trams and chucks
Figure 51 - Trammel.

Vernier Calipers

Vernier calipers (Figure 52) work like slide calipers. The Vernier calipers can make very accurate outside or inside measurements. A Vernier caliper is used by loosening the two locking screws, allowing the movable jaw to slide along the rule until desired position is obtained. The locking screw is then retightened securing the movable jaw. Any fine adjustments to the Vernier scale are made using adjustment control. The locking screw is then secured and Vernier caliper is ready to read.

Illustration of a  Vernier caliber showing the locking screw, scale, movable jaw and adjustment control
Figure 52 - Vernier caliper.

How to Read a Vernier Caliper

To read a Vernier caliper (Figure 53), you must be able to understand both the steel rule and Vernier scales. The steel rule is graduated in 0.025 of an inch. Every fourth division (representing a tenth of an inch) is numbered.

Illustration showing how to read a Vernier caliper
Figure 53 - Reading a Vernier caliper.

The Vernier scale is divided into 25 parts and numbered 0, 5, 10, 15, 20, and 25. These 25 parts are equal to 24 parts on the steel rule. The difference between the width of one of the 25 spaces on the Vernier scale and one of the 24 spaces on the steel rule is a thousandth of an inch.

Read the measurement as shown in Figure 53.

Read the number of whole inches on the top scale to the left of the Vernier zero index and record: 1.000 inch.

Read the number of tenths to the left of the Vernier zero index and record: 0.400 inch.

Read the number of twenty-fifths between the tenths mark and the zero index and record: 3 x .025 = .075 inch.

Read the highest line on the Vernier scale (3) that lines up with the lines on the top scale and record (Remember 1/25 = 0.001 inch): 11/25 or 0.011 inch.

TOTAL: 1.486 inches.

Most Vernier calipers read outside on one side and inside on the other side. If a scale isn't marked, and you want to take an inside measurement, read the scale as you would for an outside diameter. Then add the measuring point allowance by referring to manufacturer's instructions. An example of the additional measurement allowance is illustrated in Table 2.

Table listing the additional measurement allowances, by size of caliper, for the Vernier caliper
Table 2 - Additional measurement allowance

How to Reading a Metric Caliper

The steel rule is divided into centimeters (cm) (Figure 54) and the longest lines represent 10 millimeters (mm) each. Each millimeter is divided into quarters. The Vernier scale is divided into 25 parts and is numbered 0, 5, 10, 15, 20, and 25.

Illustration showing how to read a Metric caliper
Figure 54 - Reading a metric caliper.

Care of Calipers

Observe the following guidelines when working with calipers:
 
  • Store calipers in separate containers provided.
  • Keep graduations and markings on all calipers clean and legible.
  • Do not drop any caliper. Small nicks or scratches can cause inaccurate measurements.
  • Protect caliper points from damage.

Micrometers

Micrometers (Figure 55) are instruments used to measure distances to the nearest one thousandth of an inch. These measurements are expressed or written as a decimal (0.0001, 0.001, 0.01), so to use them you must know how to read and write decimals. There are four types of micrometer calipers, commonly called micrometers or simply mikes: the outside micrometer, the inside micrometer, the depth micrometer, and the screw thread micrometer.

Illustrations showing common types of micrometers, including screw thread micrometers and depth micrometers
Figure 55 - Common types of micrometers.

Outside Micrometers

The outside micrometer (Figure 56) is used for measuring outside dimensions, such as the outside diameter of a piece of round stock or the thickness of a piece of flat stock, to an accuracy of 0.001 of an inch.

Illustration of an outside micrometer showing the anvil, spindle,locknut, sleeve, thimble and ratchet stop
Figure 56 - Outside micrometer.

Inside Micrometers

Inside micrometers (Figure 57) are used to measure an inside diameter to an accuracy of 0.001 of an inch. Inside micrometers have a range of 0.500 inch, when used with 1/2-inch spacers.
Illustration of an outside micrometer showing a selection of spindles, spindle locking screw, sleeve and thimble
Figure 57 - Outside micrometer.

Depth Micrometers

Depth micrometers (Figure 58) are used to measure depths to an accuracy of 0.001 inches.

Illustration of a Depth micrometer used to measure depths to an accuracy of 0.001 inches.
Figure 58 - Depth micrometer.

Screw Thread Micrometers

The screw thread micrometer (shown in Figure 54) is used to determine the pitch diameter of screws.

How To Select the Proper Micrometer

The types of micrometers commonly used are made so that the longest movement that the micrometer spindle or rod can make is 1 inch. This movement is called the range; for example, a 2-inch micrometer has a range of from 1 to 2 inches, and can only measure work with a thickness or diameter within that range. A 6-inch micrometer has a range from 5 to 6 inches, and will measure only work between 5 and 6 inches thick. The frames of micrometers, however, are available in a wide variety of sizes, from 1 inch up to as large as 24 inches.

It is necessary, therefore, that the mechanic first find the approximate size of the work to the nearest inch, and then select a micrometer that will fit it. For example, to find the exact diameter of a piece of round stock, use a rule and find the approximate diameter of the stock. If it is found to be approximately 3 1/4-inches, a micrometer with a 3- to 4-inch range would be required to measure the exact diameter. Similarly, with inside and depth micrometers, rods of suitable lengths must be fitted into the tool to get the approximate dimension within an inch, after which the exact measurement is read by turning the thimble. The size of a micrometer indicates the size of the largest work it will measure.

How to Read a Standard Micrometer

The sleeve and thimble scales of a micrometer (Figure 59) have been enlarged and laid out for demonstration. Reading a micrometer is only a matter of reading the micrometer scale or counting the revolutions of the thimble and adding any fraction of a revolution. To understand these scales, you need to know that the threaded section on the spindle, which revolves, has 40 threads per inch. Therefore, every time the thimble completes a revolution, the spindle advances or recedes 1/40 inch, or 0.025 inch.

Illustration showing how to read th sleeve and thimble scales of a micrometer.
Figure 59 - Sleeve and thimble scales of a micrometer.

Note the horizontal line on the sleeve is divided into 40 equal parts per inch. Every fourth graduation is numbered 1, 2, 3, 4, and so on, representing 0.100, 0.200, 0.300, and 0.400 inch, respectively. When you turn the thimble so its edge is over the first sleeve line past the 0 on the thimble scale, the spindle has opened 0.025 inch. If you turn the spindle to the second mark, it has moved 0.025 inch plus 0.025 inch, or 0.050 inch. When the beveled edge of the thimble stops between graduated lines on the sleeve scale, you must use the thimble scale to complete your reading. The thimble scale is divided into 25 equal parts; each part or mark represents 1/25 of a turn; 1/25 of 0.025 inch equals 0.001 inch.

Note that in Figure 60 every fifth line on the thimble scale is marked 5, 10, 15, and so on. The thimble scale permits you to take very accurate readings to the thousandths of an inch.

Illustration of enlarged micrometer sleeve and thimble scales
Figure 60 - Enlarged micrometer scale.

The enlarged scale in Figure 60 can help you understand how to take a complete micrometer reading to the nearest thousandth of an inch.

The thimble is turned far enough to expose the 7 on the sleeve scale but not far enough to expose the first mark after the 7. Therefore, the measurement must be between 0.700 inch and 0.725 inch. Exactly how far between 0.700 inch and 0.725 inch must be determined from the thimble scale.

As you can see, the thimble has been turned through 12 spaces of its scale, and the 12th graduation is lined up with the reference line on the sleeve. When the value on the sleeve scale is added to the value on the thimble scale that is lined up with the reference line on the sleeve scale, the space between the anvil and spindle must be 0.712 inch (seven hundred twelve thousandths of an inch).

How To Read a Vernier Micrometer

Many times you are required to work to exceptionally precise dimensions. Under these conditions it is better to use a micrometer that is accurate to ten thousandths of an inch. This degree of accuracy is obtained by the addition of a Vernier scale.

The Vernier scale of a micrometer (Figure 61) furnishes the fine readings between the lines on the thimble rather than requiring you to estimate the reading. The 10 spaces on the Vernier are equivalent to 9 spaces on the thimble. Therefore, each unit on the Vernier scale is equal to 0.0009 inch, and the difference between the sizes of the units on each scale is 0.0001 inch.

Illustration of the Vernier scale of a micrometer.
Figure 61 - Vernier scale of a micrometer.

When a line on the thimble scale does not coincide with the horizontal reference line on the sleeve, you can determine the additional spaces beyond the readable thimble mark by finding which Vernier mark matches up with a line on the thimble scale. Add this number, as that many ten thousandths of an inch, to the original reading.

In Figure 62, see how the second line on the Vernier scale matches up with a line on the thimble scale. This line means that the 0.011 mark on the thimble scale has been advanced an additional 0.0002 beyond the horizontal sleeve line. When you add this number to the other readings, the reading is 0.200 + 0.075 + 0.011 + 0.0002, or 0.2862, as shown.

Illustration showing how to read a Vernier micrometer scale
Figure 62 - Reading a Vernier scale.

How To Read a Metric Micrometer

The same principle is applied in reading the metric graduated micrometer (Figure 63), but the following changes in graduations are used:
Illustration showing how to read a Metric micrometer
Figure 63 - Metric micrometer.

The pitch of the micrometer screw is 0.05 mm. One revolution of the spindle advances or withdraws the screw a distance equal to 0.5 mm.

The barrel is graduated in millimeters from 0 to 25. It takes two revolutions of the spindle to move the barrel 1 mm.

The thimble is graduated in 50 divisions with every fifth line being numbered.
Rotating the thimble from one graduation to the next moves the spindle 1/50 of 0.5 mm, or 1/100 mm. Two graduations equal 2/100 mm, and so forth.

The thimble is turned far enough to expose the 20 on the sleeve scale. The number of lines visible between the number 20 and the thimble edge is 2, which is equivalent to 2 mm. The line on the thimble coincides with the long line in the barrel, 36 or 0.36 mm. When you add the measurements together, the reading is 20 + 2 + 0.36, or 22.36 mm.

When using a Metric micrometer, remember 1 revolution is 0.5 mm. It takes 2 revolutions to move 1 mm.

How To Care for Micrometers

Observe the following guidelines when working with micrometers:
 
  • Coat metal parts of all micrometers with a light coat of oil to prevent rust.
  • Store micrometers in separate containers provided by manufacturer.
  • Keep graduations and markings on all micrometers clean and legible.
  • Do not drop any micrometer. Small nicks or scratches can cause inaccurate measurements.

Surface, Depth and Height Gauges

Surface Gauges

A surface gauge (Figure 64) is a measuring tool used to transfer measurements to work by scribing a line, and to indicate the accuracy or parallelism of surfaces. The surface gauge consists of a base with an adjustable spindle to which may be clamped a scriber or an indicator.

Picture of a Surface gauge showing the base, gauge pins and indicator

Figure 64 - Surface gauge.

Surface gauges are made in several sizes and are classified by the length of the spindle.

The smallest spindle is 4 inches long, the average 9 to 12 inches, and the largest 18 inches. The scriber is fastened to the spindle with a clamp. The bottom and the front end of the base of the surface gauge have deep V-grooves. The grooves allow the gauge to measure from a cylindrical surface.

The base has two gauge pins. They are used against the edge of a surface plate or slot to prevent movement or slippage.

Rule Depth Gauge

A rule depth gauge (Figure 65) measures the depth of holes, slots, counterbores, and recesses. Some rule depth gauges can also be used to measure angles. This measurement is done by using the angle marks located on the sliding head. The rule depth gauge is a graduated rule with a sliding head designed to bridge a hole or slot. The gauge holds the rule at a right angle to the surface when taking measurements. This type has a measuring range of 0 to 5 inches. The sliding head has a clamping screw so that it may be clamped in any position. The sliding head is flat and perpendicular to the axis of the rule. It ranges in size from 2 to 2 5/8 inches wide and from 1/8 to 1/4 inch thick.

Picture of a Rule depth gauge showing the graduated rule, sliding head, and angle marks
Figure 65 - Rule depth gauge.

Micrometer Depth Gauge

The micrometer depth gauge (Figure 66) consists of a flat base that is attached to the barrel of a micrometer head. These gauges have a range from 0 to 9 inches, depending on the length of extension rod used. The hollow micrometer screw has a 1/2- or 1-inch range. Some are provided with a ratchet stop. The flat base ranges in size from 2 to 6 inches. Several extension rods are supplied with this type gauge.

Picture of a Micrometer depth gauge showint the head and base

Figure 66 - Micrometer depth gauge.

Vernier Depth Gauge

The Vernier depth gauge (Figure 67) consists of a graduated scale either 6 or 12 inches long. It also has a sliding head similar to the one on the Vernier caliper.

The sliding head is designed to bridge holes and slots. The Vernier depth gauge has the range of the rule depth gauge. It does not have quite the accuracy of a micrometer depth gauge. It cannot enter holes less than 1/4 inch in diameter. However, it will enter a 1/32-inch slot. The Vernier scale is adjustable and may be adjusted to compensate for wear.

Picture of a Vernier depth gag showing the graduated scale and base
Figure 67 - Vernier depth gauge.

Dial Depth Gauge

Dial depth gauges (Figure 68) are for rapidly checking depths of holes, recesses, slots, scratches, and paint thickness. It should be noted that measurements made with depth gauges should be on a longitudinal axis. The depth gauge will give direct readings on the dial in half thousands of an inch (0.0005 inch); press the push button down until the measuring rod contacts the work and read the depth on the dial.

Picture of Dial depth gauge.
Figure 68 - Dial depth gauge.

Height Gauge

A height gauge (Figure 69) is used in the layout of jigs and fixtures. On a bench, it is used to check the location of holes and surfaces. It accurately measures and marks off vertical distances from a plane surface.

Picture of a Height gauge used in the layout of jigs and fixtures

Figure 69 - Height gauge.

The Vernier height gauge is a caliper with a special base to adapt it for use on a surface plate. Height gauges are available in several sizes. Most common are the 10-, 18-, and 24-inch gauges in English measure. The most common metric gauges are the 25- and 46 centimeter sizes. Height gauges are classified by the dimension they will measure above the surface plate. Like the Vernier caliper, height gauges are graduated in divisions of 0.025 inch. Its Vernier scale is divided into 25 units for reading thousandths of an inch.
Surface Plate

A surface plate (Figure 70) provides a true, smooth, plane surface. It is often used as a level base for surface and height gauges from which to make accurate measurements. Surface plates are usually made of close grained cast iron, are rectangular in shape, and come in a variety of sizes.

Picture of a Granite surface plate used to provide a true surface for a Height gauge

Figure 70 - Granite surface plate.

How to Use the Surface, Depth, and Height Gauges

Follow these steps to use surface, depth, and height gauges properly:

How To Use a Surface Gauge

Setting the surface gauge to transfer a 4-inch vertical measurement is illustrated in Figure 71.

Illustration showing how to use a surface gauge.

Figure 71 - Using a surface gauge.

How To Use a Rule Depth Gauge

A method of using a rule depth gauge to measure the distance from a surface to a recessed point is illustrated in Figure 72.

Illustration showing how to use a depth rule gauge.

Figure 72 - Using a depth rule gauge.

How To Use a Micrometer Depth Gauge

An example of measuring projection depth with micrometer depth gauge is shown in Figure 73.

Illustration showing how to using a micrometer depth gauge.
Figure 73 - Using a micrometer depth gauge.

How To Use a Vernier Depth Gauge

In Figure 74, using a Vernier depth gauge to measure the depth of a hole from a given surface is illustrated.

Illustration showing how to use a Vernier depth gauge.

Figure 74 - Using a Vernier depth gauge.

How To Use a Dial Depth Gauge

In Figure 75, measuring depths of holes, recesses, slots, scratches, and paint thickness with a dial depth gauge is illustrated.

Illustration showing how to use a dial depth gauge.

Figure 75 - Using a dial depth gauge.

How To Use a Height Gauge

Using a height gauge to measure a vertical distance from a plane surface is shown in Figure 76.

Illustration showing how to use a height gauge.

Figure 76 - Using a height gauge.

Care of Surface, Height, and Depth Gauges

Observe the following guidelines when working with surface, height, and depth gauges:
  • Coat all metal parts of gauges with a light coat of oil to prevent rust.
  • Carefully store gauges when not in use. Use separate containers if provided by manufacturer.
  • Keep graduations and markings clean and legible.
  • Do not drop any gauge. Small nicks and scratches can cause inaccurate measurements.
  • Protect all pointed gauge parts from damage.

Miscellaneous Measuring Gauges and Layout Tools

Thickness (Feeler) Gauges

Thickness (feeler) gauges (Figure 77) are made in many shapes and sizes; usually 2 to 26 blades are grouped into one tool and graduated in thousandths of an inch.
 
 

Picture of a Feeler gauge fanned out

Figure 77 - Feeler gauge.

Most thickness blades are straight, while others are bent at the end at 45-degree and 90-degree angles. Some thickness gauges are grouped so that there are several short and several long blades together. Thickness gauges are also available in single blades and in strip form for specific measurements. For convenience, many groups of thickness gauges are equipped with a locking screw in the case that locks the blade to be used in the extended position.

These gauges are fixed in leaf form, which permits the checking and measuring of small openings such as contact points, narrow slots, and so forth. They are widely used to check the flatness of parts in straightening and grinding operations and in squaring objects with a try square.

Center Gauge

The center gauge (Figure 78) is graduated in fourteenths, twentieths, twenty-fourths, and thirty-seconds of an inch. The back of the center gauge has a table giving the double depth of thread in thousandths of an inch for each pitch. This information is useful in determining the size of tap drills. Sixty degree angles in the shape of the gauge are used for checking Unified and American threads as well as for older American National or U.S. Standard threads and for checking thread cutting tools.

Picture of both sides of a  Center gauge used for checking Unified and American threads as well as for older American National or U.S. Standard threads

Figure 78 - Center gauge.

Screw Pitch Gauges

Screw pitch gauges (Figure 79) are made for checking the pitch of U.S. Standard, Metric, National Form, V-form, and Whitworth cut threads. These gauges are grouped in a case or handle, as are the thickness gauges. The number of threads per inch is stamped on each blade. Some types are equipped with blade locks. The triangular shaped gauge has 51 blades covering a wide range of pitches, including 11 1/2 and 27 threads per inch for V-form threads. Screw pitch gauges are used to determine the pitch of an unknown thread. The pitch of a screw thread is the distance between the center of one tooth to the center of the next tooth.

Picture of a Screw pitch gauge made for checking the pitch of U.S. Standard, Metric, National Form, V-form, and Whitworth cut threads.

Figure 79 - Screw pitch gauge.

Small Hole Gauge Set

Small hole gauges (Figure 80) are adjustable, having a rounded measuring member. A knurled screw in the end of the handle is turned to expand the ball-shaped end in small holes and recesses. A micrometer caliper is used to measure the ball end. Maximum measuring capacity is 1/2 inch. This set of four or more gauges is used to check dimensions of small holes, slots, grooves, and so forth from approximately 1/8 to 1/2 inch in diameter.

Picture of a set of 4 Small hole gauges.

Figure 80 - Small hole gauges.

Telescoping Gauges

Telescoping gauges (Figure 81) are used to gauge larger holes and to measure inside distances. These gauges are equipped with a plunger that can be locked in the measuring position by a knurled screw in the end of the handle. Maximum measuring capacity is 6 inches. Measurements must be calipered on the gauge by a micrometer, as in the case of the small hole gauges. They are also used when measurements cannot be taken with a standard micrometer. Telescoping gauges are particularly adaptable for roughly bored work and odd sizes and shapes of holes. Compress the plungers and lock them by turning the handle screw.

Picture of a set of 5 Telescoping gauges shown the handles and knurled screws
Figure 81 - Telescoping gauges.

Thread Cutting Tool Gauges

Thread cutting tool gauges (Figure 82) are hardened steel plates with cutouts around the perimeter. Each cutout is marked with a number that represents the number of threads per inch.

These gauges provide a standard for thread cutting tools. They have an enclosed angle of 29 degrees and include a 29-degree setting tool. One gauge furnishes the correct form for square threads and the other for Acme standard threads.

Picture of a Thread cutting tool gauge
Figure 82 - Thread cutting tool gauges.

Fillet and Radius Gauges

The blades of fillet and radius gauges (Figure 83) are made of hard rolled steel. The double ended blades of the gauge have a lock which holds the blades in position. The inside and outside radii are on one blade on the gauge. Each blade of each gauge is marked in sixty-fourths. Each gauge has 16 blades.

Picture of a double sided set of Fillet and radius gauges.

Figure 83 - Fillet and radius gauges.

Drill Point Gauge

The drill point gauge (Figure 84) consists of a 6-inch hook rule with a 59 degree sliding head that slides up and down the rule. The sliding head can be locked at any position on the rule and is graduated in thirty-seconds of an inch. This gauge is used to check the accuracy of drill cutting edges after grinding. It is also equipped with a 6-inch hook rule. This tool can be used as a drill point gauge, hook rule, plain rule, and a slide caliper for taking outside measurements.

Picture of Drill point gauge used to check the accuracy of drill cutting
Figure 84 - Drill point gauge.

Wire Gauges

A wire gauge (Figure 85) is circular in shape with cutouts in the outside edge. Each cutout gauges a different size wire, from 0 to 36 of the English Standard Wire Gauge. A separate gauge is used for American standard wire and another for U.S. Standard sheet and plate iron and steel.

Similar gauges are also used to check the size of hot and cold rolled steel, sheet and plate iron, and music wire.

Picture of a round Wire gauge

Figure 85 - Wire gauge.

Drill Gauges

The twist drill and drill rod gauge (Figure 86) has a series of holes with size and decimal equivalents stamped adjacent to each hole. One gauge measures drill sizes numbers 1 to 60; the other gauge measures drill sizes 1/16 to 1/2 inch in 1/64-inch intervals. Drill gauges determine the size of a drill and indicate the correct size of drill to use for given tap size. Drill number and decimal size are also shown in this type gauge. Letter size drill gauges are also available. Each drill hole is identified by a letter instead of a number, decimal, or fraction.

Picture of a Drill gauge.
Figure 86 - Drill gauge

How To Use a Thickness Gauge

Thickness (feeler) gauges are used in one of two ways: as a means for determining a measure or a means for adjusting to a definite limit (Figure 87). A thickness gauge is used to check piston ring gap clearance in a cylinder bore.

A long blade thickness gauge is used to determine the fit between large mating surfaces. By combining blades it is possible to obtain a wide variation of thickness.

Illustration of a mechanic using a thickness, or feeler gauge

Figure 87 - Using thickness (feeler) gauges.

How To Use a Center Gauge

The center gauge (Figure 88) is used to set thread cutting tools. Four scales on the gauge are used for determining the number of threads per inch. The gauge is also used to check cut threads and the scales are used to measure threads per inch.

Illustration showing how to use a Center gauge

Figure 88 - Using a center gauge.

How to use a Screw Pitch Gauge

If the pitch of a thread is not known, it can be determined by comparing it with the standards on the various screw pitch gauges (Figure 89).

1. Place a blade of a gauge over the threads and check to see whether it meshes; if not, successively check each blade of the gauge against the thread until it meshes.

2. The pitch can be read off the correct blade. The blades are made pointed so that they can be inserted in small nuts to check inside threads as
well as outside threads.

Illustration showing how to use a screw pitch gauge.
Figure 89 - Using a screw pitch gauge.

How To Use a Small Hole Gauge

The small hole gauges perform the same function as telescoping gauges (Figures 90 and 91), except that they are used in smaller work.

1. Fit the ball-shaped point into the hole or slot (Figure 90).

Illustration showing how to use a Small hole gauge
Figure 90 - Using a small hole gauge.

2. Expand the ball-shaped end by turning the screw at the end of the handle.

3. Use micrometer to gauge the measurement.

How To Use a Telescoping Gauge

1. Loosen the knurled nut at the end of the handle (Figure 91).

2. Slightly tilt telescoping gauge 5 to 10 degrees and lower into object to be measured.

3. Tighten knurled nut.

4. Remove gauge by pulling across center line as indicated by arrow.

Illustration showing how to use a  a Telescoping gauge.
Figure 91 - Using a telescoping gauge.

How To Use a Fillet and Radius Gauge

1. A double ended radius gauge blade is used to check the inside corner or fillet of a machined part (Figure 92). Each blade can be locked in position by tightening the clamp.

2. These gauges can be used in any position and at any angle for both inside and outside radii.

Illustration showing how to use a fillet and radius gauge.

Figure 92 - Using a fillet and radius gauge.

How To Use a Drill Point Gauge

The method for sharpening the cutting edges of a drill is to do one lip at a time. Each lip must have the same length and have the same angle in relation to the axis of the drill. Set the sliding head securely on the rule at the mark equal to the length of the drill. Place the drill vertically against the rule so that the drill lip contacts the 59-degree angle of the sliding head (Figure 93). Hold up to light; correct angle is obtained when no light is seen between gauge and drill.

Illustration showing how to use a Drill point gauge
Figure 93 - Using a drill point gauge.

How To Use a Wire Gauge

Determine the size of both sheet stock and wire by using a correct sheet and plate or wire gauge (Figure 94).

Illustration show how to use a wire gauge.

Figure 94 - Using a wire gauge.

How To Use a Drill Gauge

The drill gauge is used to determine the size of a drill (Figure 95). Insert the drill into the appropriate sized hole. A chart on the gauge indicates the correct size of drill to use for a given tap size.

Illustration showing how to use a drill gauge

Figure 95 - Using a drill gauge.

Care of Gauges and Layout Tools

Observe the following guidelines when working with gauges and layout tools: 
  • Exercise care when using thickness gauges to measure clearance of knives and cutters on machines. Do not lower knife on thickness blade and then try to remove the gauge. The blade may be shaved off if it is too tight. Never use gauges for cleaning slots or holes. When blades are damaged or worn they should be replaced. Blades in a case are removed by loosening the clamp and sliding out the damaged blade. Insert new blade and tighten clamp.
  • Always coat metal parts of all gauges with a light film of oil when not in use to prevent rust. Store gauges in separate containers. Do not pile gauges on each other.
  • Always return blades of leaf-type gauges to case after use.
  • Keep graduations and markings on all gauges clean and legible.
  • Do not drop any gauge. Small scratches or nicks will result in inaccurate measurements.

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