[Healeys] Generator nut size?

[Mike Tobin]

I done went and lost the nut holding the pulley and fan on the generator
shaft.  Moss shows three choices with no explanation so I order all of them
(cheap) and none were even close ( two were 3/8" and one was 7/16").  The
factory parts list # is LNZ206 which Google tells me is 3/8" UNF.  The
shaft is like 5/8" fine (I don't have a nut or die on had big enough to try
on it).
When I started this project I had no idea it would be the fasteners that
would drive me nuts (as it were).
Cheers,
Mike Tobin