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

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

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

3-14

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