Whit thread has a 55 deg form UNC has a 60 deg at 1/4 dia is same and tpi is the same after 70 years and with the original taps not I suppose brand new a blind man would be pleased to see the difference in soft alloy. To say nothing of which taps or dies were used on the stud -perhaps a replacementFor us non engineering types, why would you use a UNC tap when it should be a BSW tap, are they identical thread forms?
There's nothing new where threads are concerned. There are square threads, both sides vertical, often used on feed screws for machines.A little off topic, but interesting (to me anyway) I have noticed that some threads used on plastic receptacles, toothpaste tubes etc. have a flat faced thread at 90 degrees for the working part of the thread with a conventional thread on the rear section, so I suppose you could describe the thread as 55/90 degree thread, I looked at it and thought it must be a far stronger thread and less likely to strip if over tightened, has this thread form been adopted in engineering yet?