The least count of a screw gauge, also known as a micrometer screw gauge, depends on the pitch of the screw and the number of divisions on the circular scale. The formula for calculating the least count of a screw gauge is:
LC = Pitch / Number of divisions on the circular scale
For example, if the pitch of the screw is 0.5 mm and there are 100 divisions on the circular scale, the least count would be:
LC = 0.5 mm / 100 = 0.005 mm
Therefore, the least count of the screw gauge in this case would be 0.005 mm. However, the actual least count of a specific screw gauge may vary depending on its design and manufacturing specifications.