Types and Uses

TM 9-243 TYPES AND USES Micrometers are instruments used to measure dis- tances to the nearest one-thousandth of an inch. The measurement is usually expressed or written as a deci- mal. There are three types of micrometers which are commonly used: the outside micrometer, the inside micrometer, and the depth micrometer. OUTSIDE MICROMETERS INSIDE MICROMETERS Inside micrometers are used to measure an inside diameter to an accuracy of .001 of an inch. ID micrometers have a range of .500 when used with one-half inch spacers. (For remaining one-half inch, see page 7-3.) DEPTH MICROMETERS Outside micrometers are used to measure an outside distance or diameter to an accuracy of .001 of an inch. Depth micrometers are used to measure depths to an accuracy of .001 inches. SELECTING THE PROPER MICROMETER The types of micrometers commonly used are made so that 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, are available in a wide variety of sizes, from 1 inch up to as large as 24 inches. The range of a 1 inch micrometer is from 0 to 1 inch. In other words, it can be used to work where the part to be measured is 1 inch or less. A 2-inch micrometer has a range from 1 inch to 2 inches, and will measure only work between 1 and 2 inches thick. A 6-inch micrometer has a range from 5 to 6 inches, and will measure only work between 5 and 6 inches thick. It 7 - 2