Question

what is the principle of micrometer screw gauge?

Answer 1

Please clarify. Your question at the moment is very vague and hard to understand.
As far as I know, a micrometer is a scientific instrument used to measure small distances. It has a calibrated screw that amplifies distances that are too small to measure directly. By rotating the screw much more than the actual distance, one can read the distance the micrometer measures.