Vortex Rifle Scope Bubble Level lets you make the most precise long-range shot. Custom-designed for precise long-range shooting, the Vortex Bubble Level ensures that the rifle is perfectly vertical. This will eliminate potential error caused by shooting a canted rifle. The Vortex Riflescope Leveling Bubble Mounts quickly and easily to the riflescope tube. Vortex understands your desire to make the most precise shot when out in the field. The Vortex Optics Scope Bubble Level is available in models to fit multiple diameters of rifle scope tubes.