Both C and D mounts have 32 TPI. The D mount is 5/8 inch. I use the old series adaptor rings to reverse mount movie and enlarging lenses on 35mm and LF cameras. A series 6 or 7 retainer ring epoxied, thread outward, on a lens board or body cap, can be used with step-up rings for about any size lens. Some old camera stores have boxes of adaptor rings hidden away somewhere to mount the lens on the retainer ring. The effective f/number is quite high with movie lenses reverse mounted for micro work. Thus, diffraction limits resolution, even when wide open.
Originally Posted by Lee L