Orion 7370 90mm ID Telescope Tube Rings Set of two cast aluminum telescope tube rings with quick-release, hinged clamp knobs and felt lining One tube ring has 1/4"-20 piggyback camera adapter post; the other has threaded 1/4"-20 socket Set of two telescope tube rings with mounting bolts and washers included Use with Orion EQ-1, EQ-2, EQ-3, or AZ-3 telescope mounts Inside ring diameter is 90mm