Jam nut for 150mm Componon (non-s)

Would this the jam nut I need for a Beseler 45 board?

Thanks in advance

Steve.

http://www.bhphotovideo.com/c/product/44932-REG/Rodenstock_453033_50mm_Thread_Metal_Jam.html

The board shouldn't matter. It's the lens itself. Measure the threaded rear of the lens.

Sorry, how do I measure it?

Easiest would be with a digital caliper. A machine shop should have something usable.
Another thing to be aware of would be the pitch of the thread. As an alternative you might try SK grimes,
they do all sort of photo related machine work & may already have a ring of the proper size.

Is this the Componon with the all silver (chrome?) barrel? I have some circa mid 1960's literature on the Componon enlarging lenses. It indicates the f/5.6 150mm Componon mounting thread is 39mm (nominal diameter) X 0.75mm pitch. This is the same specification as the mounting thread for the No. 1 Copal and Compur shutters so a retaining ring/jamb nut for one of these shutters should fit. "Should" is an important word here. It would be ideal to have your lens in hand to try the retaining ring on, or at least be sure you can return for a refund if it doesn't fit.
David