Inside micrometers are precision measuring instruments fit to test the internal width of a piece, or better the diameter of a hole.
Devoid of frame and anvil, the main body consists of a cylinder coaxial to the sleeve of reading device. Inside, a rod commands the feelers sticking out radially to the instrument axis. Feelers can be small-levelled cylinders, rounded cylinders or hemispheres. For construction features of this type of micrometers, their measuring range is generally very small.