2 = 0.200 in
Number of lines
visible between the
No 2 and thimble
1 = 0.025 in
The line on the thimble
that coincides with or
has passed the
revolution or long line
in the barrel............................
16 = 0.016 in
= 0.241 inch
(b) Reading metric micrometer. The same principle is applied in reading
the metric graduated micrometer, but the following changes in graduations should be
noted to avoid confusion:
1. The pitch of the micrometer screw is 0.5mm. One revolution of
the spindle advances or withdraws the screw a distance equal to 0.5mm.
2. The barrel is graduated in millimeters, from 0 to 25; it takes
two revolutions of the spindle to move 1mm.
The thimble is graduated in 50 divisions with every fifth line
4. Rotating the thimble from one graduation to the next moves the
spindle 1/50 of 0.5mm, or 1/100mm. Two graduations equal 2/100mm, and so forth.
(c) Adjusting micrometer caliper to work.
1. A, figure 58, shows the proper way to hold a micrometer caliper
in checking a small part. Hold the part in one hand. Hold the micrometer in the
other hand so that the thimble rests between the thumb and the forefinger. The
third finger is then in a position to hold the frame against the palm of the hand.
The frame is supported in this manner and makes it easy to guide the work over the
anvil. The thumb and forefinger are in position to turn the thimble either
directly or through the ratchet and bring the spindle over against the work.
2. On larger work, it is necessary to have the work stationary and
positioned to permit access to the micrometer. The proper method of holding a
micrometer when checking a part too large to be held in one hand is shown in B,
figure 58. The frame is held by one hand to position it and to locate it square to
the measure; surface. The other hand operates the thimble either directly or
through the ratchet. A large flat part should be checked in several places to
determine the amount of variation.
3. To gage a shaft as shown in C, figure 58, the frame is held by
one hand while the thimble is operated by the other. In gaging a cylindrical part
with a micrometer it is necessary to "feel" the setting to be sure that the spindle
is on the diameter, and also to check the diameter in several places to determine
the amount of out-of-roundness.