General
1-23
Metric micrometer
The standard metric micrometer (Figure
24) is accurate to one one-hundredth of
a millimeter (0.01mm).
The sleeve line is graduated in millimeter
and
half millimeter increments. The marks on
the upper half of the sleeve line equal
1.00 mm. Each fifth mark above the
sleeve line is identified with a number.
The number sequence depends on the
size of the micrometer. A 0-25 mm
micrometer, for
example, will have sleeve marks
numbered 0
through 25 in 5 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 complete turn of the
thimble aligns its 0 mark with the first
line on the 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.
4. Add the readings from Steps 1-3.
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.
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