Hi.
I've come across an ancient turner-reich triple convertible lens that I'd really like to use on
my 8x10 camera. Unfortunately, it has no retaining ring. It is a rather large lens; 18 inches and 14 inches. When both elements are fitted, it is pleasantly wider than my Fuji 300; I do not know what focal length exactly.

I have tried numerous times to find a ring. The ring for my Fuji would fit perfectly, if not for the fact that the thread on the turner-reich is much coarser. I don't want to spend a fortune having one custom made.

Suggestion?