Axle drive flanges what thread?

[Lotz-A-Landies]

Have been finishing off the wheel stations on an SIIB pre-delivery to a buyer and a stud threaded out of the hub. Given the stresses on the front wheels of a forward control I decided to (attempt) to fit a pair of late SIIa hubs with press in 9/16 studs. Having done one side I now find that 5 of the drive flange bolts have broken off inside the hub. I drilled the bolts and next step is to re-tap the threads. The bolts are 3/8" and 20TPI but I'm unsure whether they are BSF or UNF.

Anyone know the truth?

3/8" UNF or 3/8" BSF?

[mick88]

3/8 BSF is 20 TPI.
3/8 UNF is 24 TPI
3/8 UNC is 16 as is BSW




Cheers, Mick.

[Lotz-A-Landies]

Thanks Mick

What is confusing me is that (I didn't have a 3/8" UNF tap handy), the 3/8" BSF tap didn't sit flush in a 20TPI SAE gauge while at the same time the same gauge sat flush in a flange bolt.

IIRC one difference between BSF and UNF is the angle of the pitch (60 degree versus 50 degree) so was thinking it would be the angle causing it not to sit flush and therefore 3/8"20 TPI UNF.

If 3/8" UNF is always 24TPI I'll re-tap BSF

[mick88]

Thanks Mick

What is confusing me is that (I didn't have a 3/8" UNF tap handy), the 3/8" BSF tap didn't sit flush in a 20TPI SAE gauge while at the same time the same gauge sat flush in a flange bolt.

IIRC one difference between BSF and UNF is the angle of the pitch (60 degree versus 50 degree) so was thinking it would be the angle causing it not to sit flush and therefore 3/8"20 TPI UNF.

If 3/8" UNF is always 24TPI I'll re-tap BSF

55 degrees for British and 60 degrees for Unified National.


Cheers, Mick.