This cast-aluminum 90mm ID Orion Telescope Tube Ring set features quick-release, hinged clamp knobs and felt lining. Designed for use with Orion telescope mounts, they fit some other brands of mounts as well. One of the two rings in the set has a 1/4"-20 piggyback camera adapter on it, the other has a threaded 1/4"-20 hole. The piggyback camera adapter can be removed for mounting an adapter plate for a guide scope on top of the tube rings. For use with Orion SkyView Pro or Atlas telescope mounts, you will also need a dovetail mounting plate.