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: Remington Models 541S & 541T (Front & Rear)Savage Models 19 & 23 (Rear)Stevens 417 (Front &Rear)Winchester Models 75 Sporter, 75 Target, & 77 (Rear)Marlin A1, 50 (Front & Rear) Notes: This is a 1-piece base for a 2-piece system.Mounting Hardware Included