A micrometre is a device used to measure small linear distances. It is a more precise instrument than a Vernier caliper but can't measure as large a range of lengths.

An object to be measured is placed between the anvil and the spindle. The thimble is adjusted until the object is almost gripped between the anvil and spindle. Turning the ratchet then adjusts the grip of the micrometre to the same tightness each time.