Figure 2-28.Inside micrometer set.
The 0.500 spacing piece is used between the spindle
and the micrometer head so the range of the micrometer
can be extended. A knurled extension handle is usually
furnished for obtaining measurements in hard-to-reach
Reading the inside micrometer. To read the inside
micrometer, read the micrometer head exactly as you
would an outside micrometer, then add the micrometer
reading to the rod length (including spacing collar,
when installed) to obtain the total measurement.
The depth micrometer is used to measure the
precise depths of holes, grooves, and recesses by using
interchangeable rods to accommodate different depth
measurements (fig. 2-21). When using a depth
micrometer, you must make sure the base of the
micrometer has a flat, smooth surface to rest on and
that it is held firmly in place to ensure an accurate
measurement (fig. 2-29).
Reading a depth micrometer. When reading a
depth micrometer, you will notice that the graduations
on the sleeve are numbered in the opposite direction of
those on an outside or inside micrometer. When you are
reading a depth micrometer, the distance to be measured
is the value that is covered by the thimble. See figure
2-30; consider the reading shown. The thimble edge is
between the numbers 4 and 5. This shows a value of at
least 0.400 inch on the sleeves major divisions. The
thimble also covers the first minor division on the
sleeve; this has a value of 0.025 inch. The value shown
on the thimble circumference scale is 0.010 inch.
Adding these three values together results in a total of
0.435 inch, or the total distance that the end of the
extension rod has traveled from the base. This
measurement added to the length of the extension rod
Figure 2-29.Using a depth micrometer.