A lathe chuck is a mechanical device used to clamp a workpiece on a machine tool. A machine tool accessory that clamps and positions the workpiece by the radial movement of the movable jaws evenly distributed on the chuck body. The chuck is generally composed of three parts: the chuck body, the movable jaw and the jaw drive mechanism. The minimum diameter of the chuck body is 65 mm and the maximum is 1500 mm, and there is a through hole in the center to pass the workpiece or bar; the back has a cylindrical or short conical structure, which is directly or through the flange to connect with the end of the machine tool spindle . Chucks are usually installed on lathes, cylindrical grinders and internal grinders, and can also be used with various indexing devices for milling and drilling machines