On 8/2/2020 6:27 PM, AMuzi wrote:

snip

I understood Mr Ruf to mean that a Sachs 2 speed of that era was
engineered with RH 10.5x26 thread.

I assume someone at F&S reasoned that your basic 9.5mm standard axle
would be less strong with a hole in the middle.Â* Once that thread is
supported with tooling the next guy asks 'why not?'

Exactly. They no doubt found that 9.5mm was not sufficient with the hole
and determined that 10.5mm was optimal and didn't want something as big
as 12mm.

I guess they also found that 10mm was not sufficient. Who knows? And it
didn't really matter. They could specify the proper nuts to be supplied.

They may have copied the Sturmey-Archer design but decided to go metric
instead of English and rounded up from 13/32" to 10.5mm.