GENERAL INFORMATION
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increments. To obtain a reading, establish the first number by the location of the 0 line on the movable
scale in relation to the first line to the left on the fixed scale. In this example, the number is 10 mm. To
determine the next number, note which of the lines on the movable scale align with a mark on the fixed
scale. A number of lines will seem close, but only one will align exactly. In this case, 0.50 mm is the
reading to add to the first number. Adding 10 mm and 0.50 mm equals a measurement of 10.50 mm.
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.
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
75-100 mm (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
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)
0.001 Indicates 1/1000 (one one-thousandth of an inch or
millimeter)
*This chart represents the values of figures placed to the right of the decimal
point. Use it when reading decimals from one-tenth to one one-thousandth of an
inch or millimeter. It is not a conversion chart (for example: 0.001 in. is not equal
to 0.001 mm).
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