Screw Gauge and its Measurement Technique


Pitch of a screw

The pitch of a screw is the distance moved along its axis by the screw in one complete rotation of its head.


Least count of a screw

The least count of a screw is the distance moved along the axis by it in rotating the circular scale by one division.


Principle of Screw gauge

The screw gauge works under the principle of the screw. When a screw is rotated in a nut, the distance moved by the tip of the screw is directly proportional to the number of rotations.


Construction of screw gauge

The Screw Gauge is an instrument to measure the dimensions of very small objects upto 0.01 mm.The Screw Gauge consists of aU 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 Ratchat arrangement (safety device) to prevent the user from exerting undue pressure.