I’ve just tried finding that company on-line but although listed it seems not to have an active web-site, or if it does it is insecure so blocked.

The Swiss thread used as the pattern for BA, is the Thury one, named after the Geneva professor of engineering who invented it.

On 23 February 2025 at 13:39 Michael Gilligan Said:

The BIG difference is the thread angle … which identifies BA at a glance.

Could you please share with us your prescription for glasses.

If you have some which can distinguish a 47.5 degree thread angle from a 55 degree from a 60 degree “at a glance” at 6mm size, then we should all buy a pair.

On 26 February 2025 at 06:09 DC31k Said:

On 23 February 2025 at 13:39 Michael Gilligan Said:

The BIG difference is the thread angle … which identifies BA at a glance.

Could you please share with us your prescription for glasses.

If you have some which can distinguish a 47.5 degree thread angle from a 55 degree from a 60 degree “at a glance” at 6mm size, then we should all buy a pair.

That’s an unexpectedly naive [or perhaps capricious] response from you, DC31K

You have put words into my my mouth !

The “glasses” are simply whatever it takes to see the thread at a suitable scale.

What matters is the perceptive ability to recognise a 47.5° angle.

MichaelG.

A bit late in the day for my suggestion, but here goes. The Tom Senior mill at the museum would need some very long gib screws because of the design but they simply have a length of brass sitting beneath the screws which extends their effective length.