### Theory:

A screw gauge is a measuring instrument that can measure the dimensions up to $$1/100th$$ of a $$millimetre$$ or $$0.01 mm$$. With the screw gauge, it is possible to measure the diameter of a thin wire and the thickness of thin metallic plates.

Construction of Screw gauge

Description of screw gauge:
The screw gauge contains a U shaped metal frame. A hollow cylinder is connected to one end of the frame. Grooves are cut on the inside surface of the cylinder through which a screw passes (shown in the above figure).
• On the cylinder parallel to the axis of the screw, there is a scale which is graded in millimetres. It is called Pitch Scale (PS).
• One end of the screw is connected to a sleeve. The head of the sleeve (Thimble) is split into $$100$$ divisions called the Head scale.
• The end of the screw has a plane surface which is known as Spindle.
• A stud called Anvil is attached to the other end of the frame, just opposite to the tip of the screw. The screw head is fitted with a ratchet arrangement (safety device) to prevent the user from exerting undue pressure.
Uses of Screw gauge:
The important uses of screw gauge are as follows,
1. It is used to measure the diameter of circular objects, mostly wires with an accuracy of $$0.001cm$$.
2. It can be used to measure the diameter of a wire.
3. It can also be used to measure the thickness of a paper.