Chuck with anti-centrifugal force feature

A chuck comprising a body with a central axis about which the chuck is adapted to be rotated, a front face, a radially movable master jaw for carrying a work-gripping member and slidable in the front face toward and away from said central axis, a jaw-actuating lever within the chuck body behind the jaw, means carried by the chuck body supporting the lever for pivoted movement about a pivot axis parallel to the front face and transverse to the direction of radial movement of the master jaw, and a lever actuator within the chuck body movable axially to pivot the lever, said lever actuator having a surface in contact with a portion of said lever to exert a force thereon, when moved, in a direction essentially axially of the chuck body, said lever having a first portion extending toward the front face from the pivot axis, a second portion longer than the first portion, extending toward the center of the chuck body from the pivot axis, and having a distal end coacting with the actuator, and a third portion elongated in a direction from the pivot axis away from the front face, longer and of greater mass than the first or second lever portion, the direction of elongation of the third portion extending from the pivot axis substantially parallel to said central axis of the chuck body when the lever is pivoted to a position in which the master jaw is moved toward the central axis.