Vernier caliper is a measuring tool for measuring length, inner and outer diameters, and depth. The vernier caliper consists of two parts: the main ruler and the cursor attached to the main ruler that can slide. The main ruler is generally in millimeters, while there are 10, 20 or 50 compartments on the cursor. Depending on the compartment, the vernier caliper can be divided into 10-degree vernier caliper, 20-degree vernier caliper, 50-degree vernier caliper, etc. The cursor is 9mm for 10-degree, 19mm for 20-degree, and 50mm for 50-degree.The indexing is 49mm. There are two pairs of movable measuring claws on the main ruler and cursor of the vernier caliper, namely the inner measuring claw and the outer measuring claw. The inner measuring claw is usually used to measure the inner diameter, and the outer measuring claw is usually used to measure the length and outer diameter.