High quality, cast-aluminum mounting rings that can be used for mounting telescope tubes on various mounts or on guidescope rails. All rings are hinged, felt-lined and have clamp-style rings for easy mounting or repositioning of the optical tube. The large clamp knob permits easy handling in all conditions, with or without gloves. The base of the rings is threaded for 6mm metric screws (not included but available at most hardware stores). Gunmetal grey finish. Available in 3 sizes: 90mm, 116mm and 136mm inner diameter.