only work between 5 and 6 inches thick.
thread micrometer), the inside micrometer, and
Therefore, in selecting a micrometer, you must
the depth micrometer (fig. 3-20). The outside
first find the approximate size of the work to the
micrometer is used for measuring outside
nearest inch, and then select a micrometer that
dimensions, such as the diameter of a piece of
fits it. For example, to find the exact diameter
round stock. The screw thread micrometer is used
to determine the pitch diameter of screws. The
of a piece of round stock, use a rule and find the
inside micrometer is used for measuring inside
approximate diameter of the stock. If it is 3 1/4
dimensions. For example, it is used to measure
inches, you need a micrometer with a 3- to 4-inch
range to measure the exact diameter. Similarly,
the inside diameter of a tube or hole, the bore of
a cylinder, or the width of a recess. The depth
with inside and depth micrometers, you must fit
rods of suitable lengths into the tool to get the
micrometer is used for measuring the depth of
approximate dimension within an inch; then, you
holes or recesses.
read the exact measurement by turning the
thimble. The size of a micrometer indicates the
Selecting the Proper Micrometer
size of the largest work it measures.
The types of micrometers commonly used are
made so that the longest movement possible
between the spindle and the anvil is 1 inch. This
Reading a Micrometer Caliper
movement is called the range. The frames of
Figure 3-21 shows an enlarged sleeve and
micrometers, however, are available in a wide
thimble scales on the micrometer caliper. To
variety of sizes, from 1 inch up to as large as
24 inches. The range of a 1-inch micrometer is
understand these scales, you need to know that
from 0 to 1 inch; in other words, it can be used
the threaded section on the spindle, which
revolves, has 40 threads per inch. Therefore, every
on work where the part to be measured is 1 inch
time the thimble completes a revolution, the
or less. A 2-inch micrometer has a range from
spindle advances or recedes l/40 inch (0.025 inch).
1 inch to 2 inches, and it measures only work
Notice that the horizontal line on the sleeve
between 1 and 2 inches thick; a 6-inch micrometer
is divided into 40 equal parts per inch. Every
has a range from 5 to 6 inches, and it measures
Figure 3-20.--Common types of micrometers.
3-14
