Abstract: A precision machine tool vise includes a body having a stationary jaw and a movable jaw mounted thereon. An actuating nut, operated by an actuating screw, engages the movable jaw and shifts the movable jaw towards and away from the fixed jaw. A cylinder housing is mounted on the vise body and bears against the outer face of the fixed jaw. The actuating screw extends through the cylinder housing and has a piston mounted thereon which is positioned within the cylinder housing. A control valve controls the flow of fluid to the cylinder housing and when actuated shifts the piston and screw towards the movable jaw. The reaction forces resulting from forward movement of the piston are transmitted from the cylinder housing to the fixed jaw and thereby prevent deflection of the fixed jaw.