A10 Full width hub Torque arm stud

[forandy]

Hello All, Can someone please help me? I've been asked by my non computer able husband to find out something, but google has failed me so I'm hoping someone here can help. He has a 1956-1957 BSA A10 with the Ariel style full width rear brake hub. At sometime in the past an incorrect sized nut has been fitted to the torque arm stud, this has damaged the threads and he wants me to source a die which he can run down this stud but I can't find out what thread it is. Can anyone please tell me? Many Thanks Pat 

[Pete A10]

I think it is 3/8 inch UNC - 16tpi

[A10 JWO]

Draganfly's website lists every nut and bolt normally including thread sizes.

[forandy]

Thank you for your help but this is my confusion. Draganfly list the nut to go on this stud as BSA  part number 21-5105 7/16 unf nyloc nut, but when you google the 21-5105 it comes up as a nut for a Bantam listed as 7/16 BSF.  Also other placed list it as BSA part number 42-6083 but I can't find out what thread that is. I was hoping that there might be someone on here who has had experience of changing the nut and knew exactly what thread it is. Thanks Pat

[MJM_58SR]

Should the part number for the bolt be 3-855

[chaz]

https://www.baxtercycle.com/product/21-5105/
Baxters normally list threads on their part numbers

another source
http://www.stevenott.com/bsatrinbw.htm