Leupold steel Standard (STD) rings and bases represent the pinnacle of versatility in our mounting system lineup. This particular model is designed to fit a Cooper 38/21/57, making it an ideal choice for standard calibers under .300 Win Mag. The STD rings are available in five different heights, allowing for precise customization to suit your setup. They are meticulously engineered to pair seamlessly with both STD 1-piece and 2-piece bases, ensuring a secure and reliable fit. Featuring a front dovetail ring that pivots, the system allows for easy lateral adjustments using the rear windage screws during bore sighting. Shims can also be incorporated, reserving the scope's elevation adjustments for use with BDC (bullet drop compensation) dials. The connection between your scope and firearm is critical, which is why Leupold mounts are built to be as rugged and dependable as the optics they secure. With an extensive range of mounting systems, you'll find the perfect fit for both your firearm and shooting style. Proudly made in the USA and backed by a lifetime guarantee, Leupold mounts are designed to withstand years of rigorous use without ever letting you down.