A depth micrometer is used to measure the depth of holes, slots, counterbores, recesses and the distance from a surface to some recessed parts. This type of micrometer is read exactly opposite to the method used to read an outside micrometer. The zero is located toward the closed end of the thimble. The measurement is read in reverse and increases in depth amount as the thimble moves toward the base of the instrument.
It has a carbide tipped spindle & a hardened measuring face.