Abstract: A high speed hydraulically actuated rotatable chuck for machine tools, permitting the high pressure clamping of elongated work pieces with capacity to be machined simultaneously at opposite ends. Two separate, axially aligned hollow work holding elements are provided, each having capacity to contract diametrically to work clamping condition, and to expand diametrically to work releasing condition. Annular actuators are mounted externally about the work holding elements, with capacity for axial movement relative thereto. A plurality of hydraulically actuated pistons are provided to advance the annular actuators, under a high, uniformly applied working pressure, to contract their work holding elements into work clamping relation. Quick-acting release means retract the actuators, upon deactivation of the pistons, to permit the work holding elements to expand to work releasing condition.