A chuck is a mechanical device used on a machine tool to clamp a workpiece. A machine tool attachment that clamps and positions the workpiece using radial movement of the movable jaws evenly distributed on the chuck body. The chuck generally consists of a chuck body, a movable jaw and a jaw drive mechanism. The chuck body has a minimum diameter of 65 mm and a maximum of 1500 mm. The center has a through hole for passing through the workpiece or the bar; the back has a cylindrical or short tapered structure, and is connected directly or through the flange to the end of the machine tool spindle. . Chucks are typically used on lathes, cylindrical grinders and internal grinders, as well as in various indexing devices for milling machines and drill presses.
From the number of chuck jaws can be divided into: two-jaw chuck, three-jaw chuck, four-jaw chuck, six-jaw chuck and special chuck. From the use of power can be divided into: manual chuck, pneumatic chuck, hydraulic chuck, electric chuck and mechanical chuck. From the structure can be divided into: hollow chuck and medium real chuck.