COMMON PARTS OF OUTSIDE MICROMETER
The U frame of micrometer is made of steel, cast steel, malleable cast iron or light alloy.
(2) Hardened anvil.
It protrudes from the frame for a distance of at least 3 mm for holding and supporting the jobs for measurement.
(3) Screwed spindle.
It does the actual measuring and possesses threads of 0.5 mm pitch.
(4) Barrel or Sleeve.
It has datum or fiducially line and fixed graduations.
This is a tubular cover fastened with the spindle and moves with the spindle. The beveled edge of the thimble is divided into 50 equal parts, every fifth being numbered.
This part is commonly recognized as friction stop of the micrometer, which acts as a precautionary measure also. It is a small extension to the thimble in which the ratchet slips when the pressure on the screw exceeds a certain amount. This produces uniform reading and prevents any damage or distortion of the instrument.
(7) Spindle clamp.
It is used to lock the instrument at any desired setting or at any particular reading .
Source A Textbook of Basic Manufacturing Processes and Workshop Technology by Rajender Singh.