Abstract: A rotary chuck with lever operated jaws, in which the levers are constructed to counteract the force-reducing effect of centrifugal force on the work-gripping jaws. The levers include a counterbalancing portion large with respect to either arm of the lever, that is wholly contained within the chuck body and extends substantially parallel to the axis of rotation of the chuck when the jaws are in a work-gripping position. A new master jaw construction facilitates mounting collet pads with a minimum of weight to reduce the adverse effects of centrifugal force.