STD(TM) Rings are precisely engineered to match up with STD(TM) 1-piece or STD(TM) 2-piece bases. Their anti-slip grooves provide exceptional grip, holding tightly to your scope, but still allowing flexibility of adjustments. 30mm High Height: 0.90" Matte Black, or gloss finish Forged and Machined steel construction Versatile, available for many different rifles Recommended Objective Size: 42-45mm Objectives will almost always use MEDIUM rings in a given style. In certain instances, 45mm scopes may require HIGH rings 50mm Objectives will almost always use HIGH rings in a given style. In certain instances, such as with extremely heavy barrels or some makes of firearm, SUPER HIGH rings may be necessary