The issue with the offerings I have seen is that the pitch is way too fine
for the large diameters.  If i recall correctly, the manufacturers in China
used the same pitch for the large ones (6 tpi or something, same as the
small ones), resulting in very weak, thin threads that sheared off.  Maybe
they have improved now, not sure (I haven’t looked at these for maybe 20
years, holy crap time flies).  As for diameter for a Moxon, I think it
depends on the size you intend to make but I’ve no experience to share.
Claudio in Waterloo