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เนื้อหาย่อ : BENCH WORK Unit l-Tl DESCRIPTION OF MEASURING TOOLS OBJECTIVES OF UNIT To acquaint the learner with the common fraction and decimal fraction systems of measuring. To explain the application of the steel rule, outside callper, inside caliper, micrometer caliper, and the steel square in measuring. 3. To explain the construction, reading, and use of the micrometer caliper. INTRODUCTORY INFORMATION The measuring of material and machined work involves the use of a number of measuring tools to secure sizes of length, wiath, thick- ness, and diameter. ome or more of these factors may be involved when determining the size of material or a plece of work. The English system of linear measure, of which the yard is the unit of length, is the standard used in American industry. In machine shop work, the more commonly used unit is the inch, the thirty-sixth part of a yard. The inch may be divided into smaller parts by means of either comon or decimal fractional divisions. The fractional divisions of an inch are found by dividing the inch into equal parts; the more comon of which are; halves, quarters, eighths, sixteenths, thirty-seconds, and sixty-fourths. When smaller units of measurement are required, the decimal system is used in which the inch is divided into tenths, hundredths, thousandths, and ten-thousandths of an inch (Figure 1). BENCH WORK TRADE THEORY SERIES 1. 2. 1,O00 .100 COMMON FRACTIONS FIG.1 TWO SYSTEMS OF DIVIDING THE INCH In machine shop it is common praotice to use fractlons of an 1nch expressed in decimals, called decimal equivalents of an inch; 1.e. 1/8" is expressed as ,125" (one hundred twenty-five thousandths of an inch), or 1/4" as .250" (two hundred fifty thousandths of an inch), etc. DECIMAL FRACTIONS