Precision-made sight bases and blades milled from high-tensile strength, rustproof alloy. Dovetailed windage and elevation adjustments have hardened gib locks. Make adjustments quickly by loosening one screw. No dovetailing of barrel necessary. Bases sold separately. Mfg: Williams Gun Sight SPECS: Bases and blades: aluminum, black anodized finish. Bases - All models except the One Inch have .5625" c-to-c hole spacing. Small - .347" radius, fits .660" to .730" dia. barrels Medium - .395" radius, fits .730" to .830" dia. barrels. Large - .440" r