SightMark Bubble Level Ring 30mm Black. Quickly attach the bubble ring to your Rifle Scope with the single bolt attachment. The bubble level ring helps distribute pressure evenly when tightening and features a highly visible center line that easily ensures the bubble is properly centered eliminating an offset Rifle Scope. Specifications for SightMark Bubble Level Rifle Scope Ring: Manufacturer: SightMark Finish: Matte Ring Height: Medium Tube Diameter: 30 mm Ring Quantity: Pair Fabric/Material: Aluminum Condition: New Weight: 0.7 oz Color: Black Mount Type: Weaver Gun Rail: Weaver Picatinny Features of SightMark Bubble Level Rifle Scope Ring Aircraft grade aluminum Single bolt attachment High visible center line Covered by the Sightmark Limited Lifetime Warranty Package Contents: SightMark Bubble Level Rifle Scope Ring SightMark SM19044: Bubble Level Ring 30mm Black