A locking collar assembly for metal forming dies includes a disc-shaped locking collar with a cylindrical outer surface closely received in a collar bore in one face of a first die member. A circular recess in the outer face of the locking collar has an internal retainer ring groove. A counterbored shaped fastener hole extends through the collar and a part of the recess, and has shank, head and shoulder portions. A socket head cap screw is inserted in the fastener hole with a threaded end anchored in a threaded end aperture in one of the guide pins, with the head seated on the shoulder of the fastener hole. A retainer ring is mounted in the collar ring groove and overlies the cap screw head to positively prevent the cap screw from unintentionally unfastening from the guide pin.