TM 9-243
READING A STANDARD MICROMETER
Reading a micrometer is only a matter of reading the
micrometer scale or counting the revolutions of the
thimble and adding to this any fraction of a revolution.
The micrometer screw has 40 threads per inch. This
means that one complete and exact revolution of the
micrometer screw (1) moves the spindle (2) away from
or toward the anvil (3) exactly 1/40 or 0.025 inch.
The lines on the barrel (4) conform to the pitch of the
micrometer screw (1), each line indicating 0.025 inch,
and each fourth line being numbered 1, 2, 3, and so
forth.
The beveled edge of the thimble is graduated into 25
parts, each line indicating 0.001 inch, or 0.025 inch
covered by one complete and exact revolution of the
thimble. Every fifth line on the thimble is numbered to
read a measurement in thousandths of an inch.
TO READ A MEASUREMENT AS SHOWN ABOVE.
Read highest figure
visible on barrel (5) . . . . . . . . . . . . . . . . 2 = 0.200 in.
Number of lines visible
between the No. 2 and
thimble edge (6) . . . . . . . . . . . . . . . . . . . 1 = 0.025 in.
The line on the thimble that
coincides with or has passed
the revolution or long line
in the barrel (7)
. . . . . . . . . . . . . . . . . . 16 = 0.016 in.
TOTAL
= 0.241 in.
7-4
