Love um, have several - NcStar Ar15 Qr Weaver Mount/ Cantilever Scope Mount Rear Ring 30mm

I have several of these on my regular scopes and red dots(using one ring),from outside of ring to outside of ring 4 inches, from inside to inside 2 1/2, you can get another 1/4 inch if you allow it to hang off its own rail a 1/4 inch, rings are 3/4 inch. I take them off and on and they hold zero. Ordering another as I write this for another red dot. LOVE THEM