Abstract: A power operated chuck in which an actuator, such as a fluid pressure actuator, causes clamping or unclamping movement of the jaws in dependence on the position of a control member, in which the power for operation of the actuator is derived from rotation of the chuck or one of two chuck body parts on a shaft of a machine tool, the power source being housed within the chuck which is thus self contained and does not require a separate power source. The power source is in the form of a plurality of fluid pressure pumps worked by a swash plate carried by the rotating chuck or a rotating chuck body part. Fluid pressure built up by the pumps is stored in a fluid pressure reservoir and used to drive the actuator. As fluid pressure is built up the swash plate is displaced to a position where, when maximum pressure has been generated, it lies perpendicular to the axis of rotation of the chuck or the rotatable chuck body part so that no further pressure is generated as the chuck continues to rotate.