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Thread Like Summary
gavin eisler, Gordon Gray
Total Likes: 7
Original Post (Thread Starter)
by Gordon Gray
Gordon Gray
What is the thread size for a BSA unit single transmission main shaft's clutch side?

I thought it was 1/2" x 20 UNF but my die in that size doesn't fit.

Snake bit in NC.......................Gordon
Liked Replies
by Steve Erickson
Steve Erickson
Good job guys! THAT is an obscure one...
1 member likes this
by gunner
All I can say is THANK YOU gunner for taking the time to help.

No problem Gordon, that list linking part numbers to thread forms has been really useful over the years, I believe it was originally posted on a site called Stainless Fasteners but then disappeared for several years when they went out of business.

I managed to save a copy of the list on my PC and then it was revived on Steve Nott 's website.

I cant imagine why BSA would choose an obscure ADM thread instead of UNF or similar, just another one of the many BSA mysteries I guess.
1 member likes this
by gunner
Gordon and anyone else, if you want a copy of the list I have PM me your email address and I will add it as an attachment and reply, the PM service on this site doesn't support attachments.
1 member likes this
by kommando
Cycle thread is normally 26tpi, but over 7/16 the option of 20 TPI is allowed, what I have found is that 20 tpi cycle and 20 tpi UNF nuts are not interchangeable.
1 member likes this
by Hugh Jörgen
Hugh Jörgen
The list is still up on stainlessbits:
1 member likes this
by BSA_WM20
ADM which stands for Admiralty is the same as BSC Coarse , or CEI 20 tpi series and has 20 TPI for around 5 sizes.
As the name suggest is was used for brass fitting on ships .
BSA used this thread on a lot of axles and some crankshafts
1 member likes this
by quinten
there is more then one instance
where bsa changed the thread-form
... but retained the existing part number .

the crankshaft rotor nut thread changed , i think in 68 , ... but not the part number .
1 member likes this
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