portion 56 projecting downwardly at its upstream end an actuating pin 58 projects from the far side of the heel over the bottom run of the trapezoidal path the position of the movable jaw does not matter and as it rounds the sprocket fig1 a gravity biases the jaw rearward to a fully open position ready to receive the neck of a bird at the top of the uphill run of the monorail track the actuating pin 58 encounters the leading downwardly curved tip of a stationary cam rail 60 whose entire upper surface is covered with a uhmw ultra high molecular weight polyethylene edge protector 62 the cam rail is substantially horizontal so that it maintains the position of the movable jaw as it moves along the top run of the path at about a constant angle with its leading edge 63 approximately parallel to the trailing edge 53 of the fixed jaw the height of the camming rail can be altered to adjust the distance between the facing edges of the stationary and movable jaws which may be necessary if bird size changes for chickens the jaws are about 7 8 inch apart when they are parallel and closed but this dimension could change if the jaws were redesigned for turkeys for example the dimension must be smaller than the width of the bird 39 s lower jaw so that the head cannot be withdrawn but not so small as to constrict the neck the cam rail has three half inch diameter supporting rods 64 welded to its bottom surface these which have threaded tips pass through holes in uhmw.