inches, in steps of 1 inch; or in sets graduated to read in units of the

metric system, from 0 to 25 millimeters by hundredths of a millimeter.

However, in most shops, standard sets up to 24 inches are more common. The

larger sizes normally come as a set with interchangeable anvils which

provide a range of several inches. The anvils have an adjusting nut and a

locking nut to permit setting the micrometer with a micrometer standard.

Regardless of the degree of accuracy designed into the micrometer, the skill

applied by each individual is the primary factor in determining the accuracy

and reliability of measurements.

Training and practice will result in

proficiency when using this tool.

(2) The types of micrometer commonly used are made so that the

longest movement possible between the anvil and the spindle is 1 inch. This

movement is called the "range". The frames of the micrometer, however, are

available in a wide variety of sizes, from 1 inch up to as large as 24

inches. The range of a 1 inch micrometer is from 0 to 1 inch. In other

words, it can be used to measure work where the part to be measured is 1

inch or less. A 2 inch micrometer will only measure work between 1 and 2

inches thick. A 6 inch micrometer has a range of from 5 to 6 inches, and

will only measure work between 5 and 6 inches thick.

It is necessary,

therefore, that the machinist first find the approximate size of the work to

the nearest inch, and then select a micrometer that will fit it.

For

example, to find the exact diameter of a piece of round stock use a rule

and-first find the approximate diameter of that stock. If it is found to be

approximately 3 1/4 inches, a micrometer with a 3 to 4 inch range would be

required to measure the exact diameter. Similarly, with the inside and the

depth micrometers, rods of suitable lengths must be fitted into the tool to

get the approximate dimension within an inch, after which the exact

measurement is read by turning the thimble.

The size of a micrometer

indicates the size of the largest work it will measure.

(3) On some outside micrometers, the

frame can be smaller, so that

the range of the micrometer is only 0 to 1/2

inch or 0 to 13 millimeters; or

it can be larger, so that the range is 23

to 24 inches.

The head has a

constant range of 0 to 1 inch. The shape of

the frame may be varied to

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