The Screw Gauge is an instrument to measure the dimensions of very small objects up-to 0.01 mm. The Screw Gauge consists of a U shaped metal frame. A hollow cylinder is attached to one end of the frame. Grooves are cut on the inner surface of the cylinder through which a screw passes. On the cylinder parallel to the axis of the screw a scale is graduated in millimeter called Pitch Scale.

One end of the screw is attached to a sleeve. The head of the sleeve is divided into 100 divisions called the Head Scale. The other end of the screw has a plane surface (S1). A stud (S2) is attached to the other end of the frame, just opposite the tip of the screw.The screw head is provided with a ratchet arrangement (safety device) to prevent the user from exerting undue pressure. 

Types: Screw Plug (Double, Ended, Go &, No Go, 6H), Screw Ring (Go or No Go, 6g)