I am modifying a Parker Hale back.sight to take modern eyepieces, The thread size is giving me some hassle as far as identification is concerned.
The diameter of the thread is 0.249" and the pitch is an excellent match to my 0 BA thread gauge..Unfortunately the diameter of an 0 BA thread should be 0.236" and indeed an 0 BA screw is a rattle fit in the threaded aperture.
I have some comprehensive books on screw threads, but I can't find anything that matches. Just wondering if Parker Hale had their own standards or is there a series of gunsmith threads that I am not aware of?