Sightmark&';s Bubble Level Rings are crafted out of aircraft-grade aluminum for a lightweight, durable design and are available in two different ring diameters, 30mm (SM19044) and 34mm (SM19045). Quickly attach the bubble ring to your riflescope 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 riflescope. Included in Package Bubble Level Ring Features Aircraft-grade aluminum Single bolt attachment High-visible center line