The Vortex Tactical 30mm Ring is a 6-screw ring that's idea for mounting red dots, red dot magnifiers and other accessories with 30mm tube diameters to your Picatinny rail. When using this ring to mount a conventional riflescope, we strongly recommend lapping the rings for a proper and secure fit for your optic. Please note this is a single ring. It comes in 5 different heights.