Nobody makes bases to fit as many guns as Weaver. Yet each base is machined to tight tolerances for a custom fit. They're 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. Custom hardened fastening screws come with every Weaver base. No.63B mountFits:Marlin 9, 45, 30AS, 36, 62, 93, 336, 375 and 444Marlin 1893/1894/1895, Glenfield 30, Zane GreyMarlin 922M and 989Mossberg 640Western Field 740