Figure 3-39. Using Outside Micrometer
Figure 3-40. Using Inside Micrometer with
be sure the tool is spanning the true diameter of a hole
or the correct width of a slot.
(b) Handle attachment. For probing a deep
hole or a restricted place, a handle attachment may be
used. The handle clamps on to the body of the
d. Reading a Standard Micrometer. Reading a
micrometer is a matter of reading the micrometer scale
or counting the revolutions of the thimble, and adding to
this any fraction of a revolution (see figure 3-41).
(1) Spindle movement. The micrometer screw
has 40 threads per inch. This means that one complete
and exact revolution of the thimble (3) moves the
spindle (2) toward or away from the anvil (1) exactly
1/40 or 0.025 inch.
(2) Barrel measurements. The following
paragraphs describe the markings which are inscribed
on the micrometer barrel and thimble (see figure 3-42).
(a) Barrel lines. The lines on the barrel (1)
conform to the pitch of the micrometer screw under the
Figure 3-41. Parts of a Micrometer