This is a Warne Scope Mounts Ring known as the 7.3 Series, model 721M.
The Rimfire rings are designed to fit a very wide selection of rifles with either a 3/8"" or 11mm dovetail. This is made possible by using a solid asymmetrical reversible clamp that can be flipped 180 degree and used on wider or narrower dovetails for the best fit.
Features:
Asymmetrical reversible side clamp fits a 3/8″ or 11mm dovetail
Uses Torx style T-15 socket cap screws 25 in/lb. of torque recommended.