General
Information
1‐19
Micrometers
A micrometer is an instrument designed
for linear measurement using the
decimal divisions of the inch or meter
(Figure 22). While there are many types
and styles of micrometers, most of the
procedures in this manual call for an
outside micrometer. Use the outside
micrometer to measure the outside
diameter of cylindrical forms and the
thickness of materials.
DECIMAL PLACE VALUES
0.1 Indicates 1/10 (one tenth of an inch
or millimeter) 0.01 Indicates 1/100 (one
one-hundredth of an inch or millimeter)
1.1
Indicates 1/1000 (one one-
thousandth of an inch or millimeter).
A micrometer’s size indicates the
minimum and maximum size of a part
that it can measure. The usual sizes
(Figure 23) are 0-25mm (0-1 in.), 25-50
mm (1-2 in.), 50-75 mm (2-3 in.) and 75-
100mm (3-4 in). Micrometers that cover
a wider range of measurements are
available. These use a large frame with
interchangeable anvils of various
lengths. This type of micrometer offers a
cost savings, but its overall size may
make it less convenient.
When reading a micrometer, numbers
are taken from different scales and
added together. The following sections
describe how to adjust, care for and
read the measurements of various types
of outside micrometers. For accurate
results, properly maintain the measuring
surfaces of the micrometer. There
cannot be any dirt or burrs between the
tool and the measured object. Never
force the micrometer to close around an
object. Close the micrometer around the
highest point so it can be removed with
a slight drag.
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