LVLING Metal Spirit Gunsmithing Tools and Accessories Bubble Level for 20mm Picatinny Weaver Rail Rifle Sight Scope Mount Compatible for 20mm lead rail Shock resistant, Can be used on real fire caliber as well as air rifles Anit-cant - make sure your scope is absolutely level Can be place before, after, or under the scope Attaches directly to weaver/picatinny dovetail to ensure bore and reticle alignment at a glance