Quote Originally Posted by Ian C View Post
The Rochester, NY made lenses regardless of brand usually used standard fractional inch diameters. The diameters vary depending on the physical size of the lens. The threads are usually 30 threads per inch 60 Unified thread.

For example, my 162/4.5 Wollensak Enlarging Raptar uses 2.0 diameter x 30 threads per inch 60 Unified thread.

I also have a flange that is 1 3/8 diameter by 30 threads-per-inch (lens unknown, but almost certainly one made in Rochester, NY) that was installed on an Omega DII/D2 lens plate.

If the threaded shank of your lens is 1 5/8 diameter, that would be about 41mm major diameter. So a reasonable guess might be 1 5/8 diameter. If you can find a mechanic with a micrometer or dial caliper, the thread diameter can be measured accurately. He or she would need an inch-designed set of thread pitch gages to determine the thread pitch accurately.
Thanks for the info.