Screw Gauge is an instrument used for measuring the diametre of thin wire or similar objects or thickness of glass plate etc. Its accuracy is upto 0.001 cm or 0.01 mm and is commonly called micrometre screw gauge. It works on principle of a screw.
Pitch of the screw is the distance travelled by the tip of the screw for one complete revolution the head. (or) The distance between two adjacent threads is also called the pitch of the screw. Smallest length that can be measured accurately using an instrument is called least count of that instrument
Least count of the screw gauge = Pitch of theScrew / No.of HeadScale Division
Thickness of a plane (or) Diameter of a wire = P.S.R + H.S.R × L.C.
If the zeroth division of the head scale does not coincide with the index line, then the screw gauge has zero error.
If the zeroth division of the head scale is above the index line of the pitch line, the error is negative and the correction is posture.
If the zeroth division of head scale is below the index line of the pitch line, the error is positive and the correction is negative.
Aim of the Experiment
To determine the diameter of a wire by screw gauge experiment
1. Screw gauge
3. Half-metre scale