Types and Purpose of Micrometer
Micrometers are made in various shapes and sizes, depending upon the purpose for which they are to be used. Some micrometers are graduated to measure in thousandths of an inch and others will measure as close as ten thousandths of an inch. Others are metric and measure in hundredths of a millimeter. There are two basic types of micrometers, with two distinct jobs. One is the outside micrometer, used to measure outside dimensions and the other is the inside micrometer, used to measure inside dimensions.
Outside micrometers. Outside micrometers are widely used in the automotive field to measure such components as crankshaft journals, piston pins, and valve stems to determine if they are within serviceability specifications. Most outside micrometers have a chrome plated or enameled steel frame to resist corrosion or tarnish.
Inside micrometers. A common inside micrometer is constructed to measure in increments of thousandths of an inch, with the smallest models having a range of one quarter inch and the largest with a one inch range. However, some inside micrometers will measure in increments of ten-thousandths of an inch. The measuring capability is extended by use of the various length extension rods. Some inside micrometers are equipped with a detachable handle that attaches to the micrometer to permit reaching into a deep bore or cavity to obtain a measurement.
Depth Micrometer. The depth micrometer is used to measure the precise depths of holes, grooves, and recesses by using interchangeable rods to accommodate different depth measurements. When using a depth micrometer, you must make sure the base of the micrometer has a flat, smooth surface to rest on and that it is held firmly in place to ensure an accurate measurement.