Discovery optical Rifle Scope Bubble Level for 1in / 30mm Tube Riflescope Anti-cant used for Shooting and Hunting Replace the 6mm diameter bubble level with 8mm bubble level to make it more visible on your rifle scope. And higher bubble level can avoid being covered by the turrets. The thickness of bottom is only 2mm(for 30mm and 34mm) or 4.4mm(for 25.4mm) so it will fit most rail system and do not need to worry about your low profile scope rings. It's full CNC machined with T6061 but not using the aluminum alloy sections. It is easy to install and to mount anywhere on scope tube left or right side, the ring is so light to carry and cannot block you view of hunting. Makes it easy to maintain a perfect horizontal hold during extreme-range shooting. And matte finish, which reduce glare so that you position can be camouflaged at all times. Viscous fluid: No matter what circumstance, it always exists one bubble.