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. Features Material – Aluminium; Style - Weaver; Fits – 418M,Marlin Models MLS-50 & MLS 54,Thompson Center Models Thunderhawk & Firehawk; Notes Two per package.; Mounting Hardware Included.; .