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. brbrSpecificationsbrbr- Base Type 2 Piece Base-br- Material Aluminumbr- Style Weaverbr- Finish Gloss BlackbrbrFits brbr- Marlin Models MLS-50 & MLS 54br- Thompson Center Models Thunderhawk & FirehawkbrbrNote Mounting Hardware Included.