Figure 3-44. Reading a Metric Micrometer
(3) Thimble graduations. The thimble (3) is
graduated in 50 divisions with every fifth line being
numbered. Each line represents a distance of 1/100, or
(4) Reading a measurement. A measurement
can be read as follows:
Read the highest whole number visible on the
barrel (5) and record ................. 20 = 20.0 mm
Count the number of lines visible between the
20 and the thimble edge (4) and record 2 = 2.0 mm
Locate the line on the thimble (3) that coincides
with or has passed the horizontal line in the
barrel (2) and record ..... 36 = 36/100 = 0.36 mm
Total all preceding measurements ..... 22.36 mm
The measurement, therefore, is 22.36 millimeters.
g. Transferring Measurements from Inside Caliper
or Inside Micrometer to Micrometer Caliper. When it
becomes necessary to transfer a measurement from an
inside caliper to an outside caliper, perform the following
procedures: TM 1-1500-204-23-9
(1) After setting inside caliper or inside
micrometer to the work, hold the micrometer caliper in
one hand and the inside tool in the other hand.
(2) Turn the thimble of the micrometer caliper
with the thumb and forefinger until the inside tool legs
lightly contact the anvil and spindle of the micrometer
(3) Hold the tips of the inside tool legs parallel
to the axis of the micrometer caliper spindle.
(4) The micrometer caliper will be accurately
set when the inside tool will just pass between the anvil
and spindle by its own weight.
h. Micrometer Adjustment and Testing. At times it
may become necessary to adjust and/or test the
accuracy of a micrometer.
(1) Adjustment. Micrometer may be adjusted to
compensate for thread wear. Adjust as follows.
(a) Unscrew thimble from barrel.
(b) Tighten the thread play adjustment nut
on the fixed nut a fraction of a turn at a time.
(c) Test the fit of the micrometer screw in
the fixed nut.
(d) Repeat the tightening and test in the
fixed nut until the operation is free from binding and
(2) Testing. A micrometer is tested for
accuracy as follows:
(a) Clean the measuring faces with a soft
cloth and examine the faces for any lint left by the cloth.
(b) Measure the length of the micrometer
test gauge of the same length as the minimum capacity
of the micrometer.
(c) The micrometer should read the exact
(d) For the 1-inch micrometer, screw the
thimble down until the spindle contacts the anvil. The
reading should be 0.000 inch.