Abstract: An improved stop mechanism for use with machinery wherein a workpiece is advanced through one or more tooling stations comprises an arm supported for limited pivotal movement about orthogonal axes. The arm is constrained for movement within a grooved block and mounted on a pin extending through coaxial conical bores formed in opposite sides of the arm. The arm is biased in a direction opposite to travel of the workpiece to a ready position in sliding contact with the workpiece until the forward end of the arm engages a predetermined notch or locating surface on the workpiece and pivotally moves therewith to a stop position. The rear end of the arm simultaneously actuates a valve, switch or other control device to initiate the desired operation on the workpiece. After completion of the desired operation, the arm is disengaged from the notch or locating surface to release the workpiece and returned to the ready position.