TM 9-243TYPES AND USESMicrometers are instruments used to measure dis-tances to the nearest one-thousandth of an inch. Themeasurement is usually expressed or written as a deci-mal. There are three types of micrometers which arecommonly used: the outside micrometer, the insidemicrometer, and the depth micrometer.OUTSIDE MICROMETERSINSIDE MICROMETERSInside micrometers are used to measure an insidediameter to an accuracy of .001 of an inch.ID micrometers have a range of .500 when used withone-half inch spacers. (For remaining one-half inch, seepage 7-3.)DEPTH MICROMETERSOutside micrometers are used to measure an outsidedistance or diameter to an accuracy of .001 of an inch.Depth micrometers are used to measure depths to anaccuracy of .001 inches.SELECTING THE PROPER MICROMETERThe types of micrometers commonly used are made sothat the longest movement possible between the spin-dle and the anvil is 1 inch. This movement is called the“range.” The frames of micrometers, however, areavailable in a wide variety of sizes, from 1 inch up to aslarge as 24 inches. The range of a 1 inch micrometer isfrom 0 to 1 inch. In other words, it can be used to workwhere the part to be measured is 1 inch or less. A 2-inchmicrometer has a range from 1 inch to 2 inches, and willmeasure only work between 1 and 2 inches thick. A6-inch micrometer has a range from 5 to 6 inches, andwill measure only work between 5 and 6 inches thick. It7 - 2
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