Mounting ring specifically designed for the Cross-Eye Periscope, but could also be used to mount other 34 mm diameter light duty accessories.  Constructed of durable glass-filled nylon.The single thumb screw makes it easy to mount on any 1913 Picatinny rail system.  Simply remove the thumb screw to open the ring and close around the Cross-Eye Periscope.  Place on the rail behind your sighting system and replace the thumb screw.  Adjust the Cross-Eye Periscope angle for natural sight alignment and hand tighten until no wobble is felt on the rail