This screw attaches the lower tang to the main receiver on the rifle. There is one screw on each side. On the 2nd model lower tang the screw was moved to the rear of the frame and changed from a 6-48 thread to a larger 3/16-36. they continued to use the larger screw throughout the end of production; Keep in mind if you have an early 2nd model serial number during the transition from 1st to 2nd you may need the 1st model lower tang screws. To be sure take your upper tang plug screw or your side plate screw and try threading it into the hole. If the screws are too large to fit in the lower tang screw hole then you will need the 1st model screw (wp601-b)
