Calipers

Calipers

— measuring instruments for determining linear dimensions with an accuracy of at least a tenth of a millimetre (although higher accuracy is also found). They are intended mainly for measuring external dimensions, although many models also provide the possibility of internal measurements at shallow depths and/or the ability to measure the depth of holes and recesses.

The design of the caliper is based on a rail (rod) with a measuring scale, along which a special frame can move freely. One measurement sponge is placed on the rod and does not move, the second is mounted on a movable frame. For internal measurements, an additional pair of jaws is provided, usually at the top of the structure. And for depth measurements, a depth gauge ruler is used, which is connected to the movable sponge and extends from the end of the rod on the opposite side of the fixed sponge; such a ruler plays the role of a kind of probe, which descends to the bottom of the hole or recess when measuring the depth.

Calipers can use a different principle of operation — mechanical or digital. For more on this, see "View of the caliper"; here we note that digital instruments are much more accurate, they often provide measurement accuracy at the level of hundredths of a millimetre (and not tenths, like "mechanics"). Such high-precision instruments are sometimes referred to as micrometer calipers and fall into one or the other category.