Hi Norm!
Brilliant ... very interesting because it rings so true!

20TPI and 26TPI are the cycle threads I know.
They remain constant over diameters.

Here, we mainly deal with BSC [British Standard Cycle] at 26TPI.

You have explained Villiers' proclivity to 20TPI.
I never knew that!

I would like to make this point to readers ...
The Imperial System was ad-hoc and gained standardization over
four decades.

The North American SAE system is by far - superior to
the baggage of development in the British system[s].
That is understandable. SAE has only 120 years' of baggage,
and three centuries of reflection.

UNF is a better fine thread than BSF
UNC is a better course thread than Whitworth.

[Linked Image]

Yes, of course I favour the Metric system.
But metric pitches are not without their historical baggage.

Threads are an interesting area - and I deal with this on a
daily basis.

Cheers
------------------------
Jack

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