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.
 
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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.