For accurate work you will need a good micrometer. These are rather expensive, but a 1 inch size and
a 2 inch size will be used often and are well worth the price. To go with these you should have a set of
inside micrometers. These come with adjusting rods to measure from 2 inches up.
For accurately measuring holes smaller than 2 inches across, a telescoping gauge should be used. This
has a handle with a telescoping head operated by a spring. Several lengths of pins fit the sliding part of
the head, and there is a locking nut at the end of the handle.
For measuring the depth of holes, a depth gauge is necessary. For very accurate work, a micrometer
depth gauge should be used. The usual run of work in a home workshop will not require the use of a
micrometer depth gauge, so one with a sliding head is good enough.
The smallest measurement in common fractions that can be made with the fixed caliper and steel rule is
1/64." To measure in thousandths and ten-thousandths, you will need a micrometer.