B-Square no gunsmithing semi-auto pistol mounts integrate with the pistol's original components to assure optimum performance with every trigger pull, superior to any grip" mounted system. Rim Fire "Sight-to-Sight" custom mounts use existing screw holes for a rock solid foundation. All B-Square mounts provide full-length ring rails for maximum eye relief adjustment. Ruger MK I/MK II Universal- (slides on receiver): For non-drilled. Ruger MK I & MK II's only. Uses existing front & rear sight screw holes. Full length and lightweight. Standard Dovetail Base.