GENERAL INFORMATION
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mm increments. This numbering sequence continues with larger micrometers. On all metric
micrometers, each mark on the lower half of the sleeve equals 0.50 mm.
The tapered end of the thimble has 50 lines
marked around it. Each mark equals 0.01 mm. One
completer turn of the thimble aligns its 0 mark with
the first line lower half of the sleeve line or 0.50mm.
When reading a metric micrometer, add the
number of millimeters and half-millimeters on the
sleeve line to the number of one one-hundredth
millimeters on the thimble. Perform the following
steps while referring to Figure 25.
1. Read the upper half of the sleeve line and count the number of lines visible. Each upper line
equals 1mm.
2. See if the half –millimeter line is visible on the lower sleeve line. If so, add 0.50mm to the reading
in Step 1.
3. Read the thimble mark that aligns with the sleeve line. Each thimble mark equals 0.01mm.
NOTE
If a thimble mark does not align exactly with
the sleeve line. Estimate the amount between
the lines. For accurate readings in
two-thousandths of a millimeter (0.002mm),
use a metric vernier micrometer.
4. Add the readings from Steps 1-3.
Standard inch micrometer
The standard inch micrometer (Figure 26) is
accurate to one-thousandth of an inch or 0.001. The
sleeve is marked in 0.025 in. increments. Every fourth
sleeve mark is numbered 1,2,3,4,5,6,7,8,9. These
numbers indicate 0.100, 0.200, 0.300, and so on.
The tapered end of the thimble has 25 lines
marked around it. Each mark equals 0.001 in. One
complete turn of the thimble will align its zero mark
with the first mark on the sleeve or 0.025 in.
To read a standard inch micrometer, perform the
following steps and refer to Figure 27.
1. Read the sleeve and find the largest number
visible. Each sleeve number equals 0.100 in.
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