Copal Compur Prontor #3 Shutter Lens Retaining Ring Brand new one set lens retaining ring for Copal, Compur, Prontor #3S, internal screw thread diameter is 60.4mm, made of aluminum with high precision machining and black finished. Please note that this is 3S retaining ring, not #3. It's for some Fujinon lenses use, like Fujinon 250mm f/6.3 etc.
eBay