is provided with a clamping surface 50 movable finger 47 can be slid longitudinally of its length from a solid line position marked a through an intermediate position marked b where it extends out over the surface 49 and thence into a clamping position marked c where it can squeeze the workpiece between the surface 50 and the surface 49 to hold it tightly during movement of the clamp in order to move the movable finger 47 the movable finger is provided with a slot 52 that rides on a pin 54 mounted on the housing 42 the movable finger 42 is held in a retracted position by a spring 55 and thus allows a workpiece to be lowered vertically onto the surface 49 of the stationary finger 46 the movable finger is extended against the force of the spring 47 by a pair of interrelated pneumatic cylinder and piston actuators 56 and 57 actuator 56 is provided with a piston 58 having a piston rod 59 that abuts against the movable finger 47 air pressure from a line 60 moves the piston 58 to the left to extend the movable finger to the left as viewed in fig3 actuator 57.