The screw gauge is an instrument used for measuring exactly the diameter of a thin wire or the width of a sheet of metal. It comprises of a U-shaped mount which is fixed with a screwed pin which is fixed to a thimble. Side by side to the axis of the thimble, a scale passed in mm is inscribed. Having a U shaped metallic mount, a screw gauge measures even the tiniest length with exact accuracy.
Just like Vernier calipers, a screw gauge also holds two scales - a key scale and an additional scale. The key scale is a millimeter scale passed to 0.5 mm, on the other hand, the additional scale is split into 50 uniform divisions. The additional scale is on the small metal cap which safeguards the finger while sewing of the screw gauge and measures hundredth of the measurement.
The mandible of the gauge is shifted revolving the thimble. The additional scale on the thimble is also termed as the Vernier revolving scale. Besides, the thimble is so adapted that 2 changes of the thimble will let the mandible to shift by 1 mm. This means that a single revolving will shift the mandibles only by 0.50 mm. The key scale rest on the part of the screw gauge termed as the “sleeve".
In order of priority to take the studies by using a screw gauge, the thing is set between the mandibles which are shifted by the thimble. The transmission button is used to set the object strongly between the mandibles. For exact reading, the thimble should be shifted until three clicks are audible from the main part of the device.
The main part of the device checks the exactness and also stops the object from getting ruined. The key scale reading is taken considering also the 0.5 mm divisions that are given below the key scale. The additional scale reading is captured by noticing the level on the thimble that coexists with the key scale on the sleeve.