Depends on whether your a purist For a start ? But there is more to a thread than just its TPI, but then I’m sure you know all of that – I would have to use 2 boxes.  Noel.

hex size is the decider. BSF is a lot larger at 3/8″ (9.53mm) while 2BA is 8.23mm so keep the BA for models where the smaller hex looks th epart and the BSF for where it does not matter.

Speaking of BA, (British Airways in this case, the threads were Unified), does anyone remember this one.

https://en.wikipedia.org/wiki/British_Airways_Flight_5390

AAIB report here

https://assets.publishing.service.gov.uk/media/5422faa7e5274a131400078d/1-1992_G-BJRT.pdf

Bill

Bill, I flew out to Canada the day after that incident, from Manchester. Never seen so many ground-crew personnel, all checking windscreens…

Rob

It might be interesting to see what is the minimum amount of kit to determine the difference.

I think a cheap USB microscope and some free software might be enough. You might have to calibrate the system by drawing a 55 degree and 47.5 degree angle on a piece of paper with a very sharp pencil.

Bonus points if you can construct either angle using a straight edge and compass (nearest the bull rules would apply if an exact construction is not possible).

Though if you are magnifying a cross section like that to find out what your thread is it kind of defeats the purpose of sorting the screws if you have to saw them all in half 😈

I have been stumped by a thread in the past that was ∅6 x 1. I had the original damaged screws I needed to replicate (for a friend) and the frame they screwed into. Tried M6 and 0BA in the holes and they did not fit. Eventually I found it was a Löwenherz thread from Europe. At just over 53° it was hard to judge by eye from similar angles but certainly would not fit M6 or 0BA parts. This was for a Victorian music box so the option of recutting the threads in the frame to M6 was a no no. So similar screws are not interchangeable in most cases.

Martin C

Jason

That one was a simple wax moulding taken from a [female] Leitz camera mount … Done to demonstrate that the thread is Whitworth form, not metric

The red wax was salvaged from some cheese and sliced with a razor blade.

… I only showed it here as an example of what 55° looks like

Perhaps you could CAD a 47.5° angle as an overlay, so that participants can see the difference for themselves.

MichaelG.

Thanks, Jason … I think most viewers could learn to ‘spot the difference’ on an image at that scale.

MichaelG.

Martin –

Did you succeed in making new Löwenherz thread screws?

While both are out of date, I would favour the BA, we have about 500000 BA screws, bolts, nuts and washers at the museum and maybe thats why I am biased. The Smart & Brown model A lathe we have uses BSF and BA threads exclusively, not counting the many mods and repairs we have made in the last 20 years which mostly use metric.

Wouldn’t we all like a shadograph to look closely at threads etc.