Higoo&reg; Bubble Level for 20mm Picatinny Waver Rail Rifle Scope Compatible for 20mm picatinny waver 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