The screw micrometer, also known as a micrometer, screw micrometer, and micrometer, is a more precise tool for measuring length than a vernier caliper. Using it, the length can be measured to an accuracy of 0.01 mm, with a measurement range of several centimeters. A part of it is processed into a thread with a pitch of 0.5 mm. When it rotates in the screw sleeve of the fixed sleeve B, it will move forward or backward. The movable sleeve C and the screw are connected as a whole, and its periphery is equally divided into 50 divisions. The total number of rotations of the screw is measured by a scribed line spaced 0.5 mm apart on the fixed sleeve, and the portion less than one revolution is measured by the scribed line around the movable sleeve. The final measurement result needs to be estimated to one decimal place.