CHAPTER 2 MEASURING TOOLS AND TECHNIQUES When performing maintenance and repair tasks on simplest and most common is the steel or wooden catapults and arresting gear equipment, you must take straightedge rule. This rule is usually 6 or 12 inches accurate measurements during inspection, to determine long, although other lengths are available. Steel rules the amount of wear or service life remaining on a may be flexible or nonflexible, but the thinner the rule particular item or to make sure replacement parts used is, the easier it is to measure accurately with it, because to repair equipment meet established specifications. the division marks are closer to the work to be The accuracy of these measurements, often affecting measured. the performance and failure rates of the concerned Generally, a rule has four sets of graduated division equipment, depends on the measuring tool you use and marks, one on each edge of each side of the rule. The your ability to use it correctly. longest lines represent the inch marks. On one edge, each inch is divided into 8 equal spaces, so each space COMMON MEASURING TOOLS represents 1/8 inch. The other edge of this side is LEARNING OBJECTIVES: Identify the divided into sixteenths. The 1/4-inch and 1/2-inch different types of measuring tools. Describe marks are commonly made longer than the smaller the uses of different types of measuring tools. division marks to facilitate counting, but the Describe the proper care of measuring tools. graduations are not normally numbered individually, as they are sufficiently far apart to be counted without You will use many different types of measuring difficulty. The opposite side of the rule is similarly tools in the daily performance of your duties. Where divided into 32 and 64 spaces per inch, and it is exact measurements are required, use a micrometer common practice to number every fourth division for caliper (mike). If you use the micrometer caliper easier reading. properly, it will allow you to measure within one ten-thousandth (0.0001) of an inch accuracy. On the There are many variations of the common rule. other hand, where accuracy is not extremely critical, a Sometimes the graduations are on one side only, common straightedge rule or tape rule will suffice for sometimes a set of graduations is added across one end most measurements. for measuring in narrow spaces, and sometimes only the first inch is divided into 64ths, with the remaining RULES AND TAPES inches divided into 32nds and 16ths. Steel tapes are made from 6 to about 300 feet in Figure 2-1 illustrates some of the commonly used length. The shorter lengths are frequently made with a straightedge and tape rules. Of all measuring tools, the curved cross section so that they are flexible enough to roll up, but remain rigid when extended. Long, flat tapes require support over their full length when measuring, or the natural sag will cause an error in reading. MEASURING PROCEDURES To take a measurement with a common rule, hold the rule with its edge on the surface of the object being measured. This will eliminate parallax and other errors that might result because of the thickness of the rule. Read the measurement at the graduation that coincides Figure 2-1.—Some common types of rules. with the distance to be measured, and state it as being so 2-1 Figure 2-2.—Measuring with and reading a common rule. many inches and fractions of an inch. (See fig. 2-2.) Always reduce fractions to their lowest terms, for Figure 2-4.—Measuring the outside diameter of a pipe. example, 6/8 inch would be called 3/4 inch. A hook or eye at the end of a tape or rule is normally part of the first measured inch. other side of the pipe. For most purposes, the measurement obtained by using this method is Bolts and Screws satisfactory. It is necessary that you know how to take this measurement, as the outside diameter of pipe is The length of bolts and screws is best measured by sometimes the only dimension given on pipe holding them up against a rigid rule or tape. Hold both specifications. the rule and the bolt or screw to be measured up to your eye level, so that your line of sight will not be in error in Inside Pipe Diameters reading the measurement. As shown in figure 2-3, the bolts or screws with countersink-type heads are To measure the inside diameter of a pipe with a measured from the top of the head to the opposite end, rule, as shown in figure 2-5, hold the rule so that one while those with other types of heads are measured corner of the rule just rests on the inside of one side of from the bottom of the head. the pipe. Then, with one end thus held in place, swing the rule through an arc and read the diameter across the Outside Pipe Diameters maximum inside distance. This method is satisfactory for an approximate inside measurement. To measure the outside diameter of a pipe, you should use some kind of rigid rule. A wooden rule or a Pipe Circumferences steel rule is satisfactory for this purpose. As shown in figure 2-4, line up the end of the rule with one side of To measure the circumference of a pipe, you must the pipe, using your thumb as a stop. Then, with the one use a flexible-type rule that will conform to the shape of end held in place with your thumb, swing the rule the pipe. A fabric or steel flexible tape rule is adaptable through an arc and take the maximum reading at the to this job. When measuring the pipe, make sure the tape is wrapped squarely around the axis of the pipe to ensure that the measurement will not be more than the Figure 2-3.—Measuring the length of a bolt or screw. Figure 2-5.—Measuring the inside diameter of a pipe. 2-2 main body of the rule. See figure 2-7. In this illustration the length of the main body of the rule is 13 inches, and the extension is pulled out 3 3/16 inches; the total inside dimension being measured is 16 3/16 inches. Notice in the circled inset in figure 2-8 that the hook at the end of the particular rule shown is attached to the rule so that it is free to move slightly. When an outside dimension is taken by hooking the end of the rule over an edge, the hook will move to locate the end of the rule even with the surface from which the measurement is being taken. By being free to move, the hook will retract toward the end of the rule when an inside dimension is taken. To measure an inside Figure 2-6.—Measuring the circumference of a pipe with a dimension using a tape rule, extend the rule between the tape rule. surfaces as shown, take a reading at the point on the scale where the rule enters the case, and add 2 inches. The 2 inches are the length of the case. The total is the actual circumference of the pipe. This is extremely inside dimension being taken. important when you are measuring a large diameter pipe. Outside Dimensions Hold the rule or tape as shown in figure 2-6. Take the reading, using the 2-inch graduation, for example, To measure an outside dimension using a tape rule, as the reference point. In this case the correct reading is hook the rule over the edge of the stock. Pull the tape found by subtracting 2 inches from the actual reading. out until it projects far enough from the case to permit In this way the first 2 inches of the tape, serving as a measuring the required distance. The hook at the end of handle, will enable you to hold the tape securely. the rule is designed so that it will locate the end of the rule at the surface from which the measurement is being Inside Dimensions taken. When taking a measurement of length, hold the tape parallel to the lengthwise edge. For measuring For an inside measurement such as the inside of a widths, the tape should be at right angles to the box, a folding rule that incorporates a 6- or 7-inch lengthwise edge. Read the dimension of the rule exactly sliding extension is one of the best measuring tools. To at the edge of the piece being measured. take the inside measurement, first unfold the folding It may not always be possible to hook the end of the rule to the approximate dimension. Then, extend the tape over the edge of stock being measured. In this case end of the rule and read the length that it extends, it may be necessary to butt the end of the tape against adding the length of the extension to the length on the another surface or to hold the rule at a starting point from which a measurement is to be taken. Figure 2-7.—Using a folding rule to measure an inside dimension. Figure 2-8.—Measuring an inside dimension with a tape rule. 2-3 Distance Measurements them with hard objects. They should preferably be kept in a wooden box when not in use. Steel or fiberglass tapes are generally used for To avoid kinking tapes, pull them straight out from making long measurements. Secure the hook end of the their cases—do not bend them backward.