Leupold 52306: Designed to accommodate firearms with unique integral mounting systems, these ringmounts are a high quality alternative to ringmounts sold by firearms manufacturers and as a no-tap mounting method for most .22 rimfire rifles with an 11mm, 13mm, 3/8\" dovetail rail. Leupold ringmounts feature superior integrity and tighter tolerances because they are machined from solid stock. Also available in Extension rings to provide 5/8\" of additional fore and aft ring spacing.