Question

what is the purpose of spring and rachet arrangement in a screw gauge

Answer 1

The rachet is provided to avoid excessive pressure on the wire.It prevents the spindle from further movement.

Answer 2

The micrometres screw gauge essentially consists of an accurate screw having about 10 or 20 threads. Ratchet also provided to avoid excessive pressure on wire. Ratchet provided at the end of the tube.
Arrangement of springs in various CASNUB trolleys according to axle load.Type of wagon.Spring nest arrangement for 20.30 axle load.
(I hope this answer is useful to you....)
(I hope this answer is useful to you....)