micrometer screwmi·crom·eter screw
The definition of a micrometer screw is a finely threaded screw with a graduated head, which is used to measure a small distance by showing exactly how far the screw has been moved in or out.
An example of a micrometer screw is what someone would use with a micrometer to find out the exact thickness of a piece of wood.
a finely threaded screw of definite pitch, with a head graduated to show how much the screw has been moved in or out: used in micrometers, etc. to give fine measurements, sometimes to .0001 of an inch