Abstract: A chuck has a chuck body, an actuating element limitedly axially displaceable in the body, a first set of guide pistons axially fixed in the actuating element, angularly spaced about the axis, and each forming a guide passage extending at a small acute angle to the chuck axis, and a second set of guide pistons limitedly axially movable in the actuating element, angularly spaced about the axis, interleaved with the axially fixed guide pistons, and each forming a guide passage extending at a small acute angle to the chuck axis. Respective jaw bolts slidable in the passages each have an outer end projecting forward from the chuck body and a rear end axially coupled to the chuck body. The outer ends of the jaw bolts of the axially fixed pistons define a fixed-jaw circle centered on the chuck axis and the outer ends of the jaw bolts of the axially movable pistons define a movable-jaw circle centered on the axis.