Each Weaver base is machined to the tightest tolerances for a custom fit. They are designed to fight the effects of recoil with a square-cut notch that precisely mates to the sturdy cross bolt in every Weaver detachable ring. Fits: Browning Lever Action (Front and Rear)Colt Coltsman round receiver (Front and Rear)Mossberg Models 810 & RM7 (Rear)Western Field 730 (Rear)Winchester Models 52 and 61 w/ an octagonal barrel (Rear) Notes: This is a 1-piece base for a 2-piece system.Mounting Hardware Included