Monstrum Level Bubble Products are built to check for proper vertical alignment of your rifle | Imperfect vertical alignment of your scope when shooting introduces scope cant error - horizontal drift of your shots due to cant - An anti-cant level bubble corrects for this issue, allowing you to quickly check for proper alignment of your rifle before each shot. | The level bubble attaches to your picatinny rail with a low profile design that slots in at the base of your of your rifle scope and can be folded up when not in use | Crafted from lightweight 6061 grade aluminum | All Monstrum optics and accessory products come with a lifetime guarantee