Leupold steel Standard (STD) rings and bases are the most versatile of any mounting system we offer. This specific model fits a Cooper 22/16/23 and is the perfect choice for standard calibers less than .300 Win. Mag. STD rings come in five different heights and are precision engineered to match up with STD 1-piece or 2-piece bases. The front dovetail ring pivots, allowing for lateral adjustment using the rear windage screws while bore sighting.