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
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