2BA versus 3/16 BSF – any real difference?

[bugbear6502Participant @bugbear6502]

I’ve been sorting through a box of small assorted bolts.

Pretty easy way to while away an hour or two with a dial caliper and a thread gauge or two.

But I’m hitting a minor (and unimportant) problem.

2BA is OD 0.1850″, or 4.70mm, thread pitch is 31.36 TPI or 0.81mm

3/16″ BSF is OD 0.1875″ or 4.76mm, thread pitch is 32 TPI or 0.79mm

Given normal bolt tolerances, are those two specifications actually different on real bolts?

The bolts I’m measuring have variability that exceeds the specification differences.

Do I just put them all in 1 box labelled?

2BA or 3/16″ BSF

[noel shelleyParticipant @noelshelley55608]

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.

[Clive FosterParticipant @clivefoster55965]

Thread angle is different so the smaller 2 BA bolt in a 3/16 BSF nut gives a significantly weaker joint with much greater tendency to unscrew.

However the really dangerous one is OBA in 1/4 BSF as the fit is even looser and strength even less. Maybe 1/3rd of BSF in BSF at best on a good day, probably less given normal tolerances.

Clive

[JasonBModerator @jasonb]

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.

[Michael GilliganParticipant @michaelgilligan61133]

For sorting … select a good BA nut, and screw each bolt into it.

No need to measure them … do it by feel.

Triage is then BA/BSF/Junk

[peak4Participant @peak4]

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

[Nigel Graham 2Participant @nigelgraham2]

Keep them separate.

The odd mixing for something quick and temporary may not matter, but would be very poor practice on finished work, leading to potential failure.

Even if that didn’t happen you could end up with a very irritating mess as some screws need that spanner, others, need this one… even on the same component like a cover or pipe flange.

For sorting by hexagon as Jason suggests, use a socket-spanner in good condition as a gauge.

[Grindstone CowboyParticipant @grindstonecowboy]

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

Rob

[Speedy Builder5Participant @speedybuilder5]

About 7 1/2 degrees

[DC31kParticipant @dc31k]

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).

[Michael GilliganParticipant @michaelgilligan61133]

As I have mentioned before … with quite modest magnification, and a little practice. it is very easy to visually distinguish between 55° and 47.5°

Measuring either is a little more difficult of course.

Here’s a starter:

.

.

MichaelG.

[JasonBModerator @jasonb]

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 😈

 

 

[JasonB]

On JasonB Said:

…if you have to saw them all in half

 

 

Written very small in the photo above is ‘wax mould’. That might be a non-destructive way.

[Martin ConnellyParticipant @martinconnelly55370]

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

[bugbear6502Participant @bugbear6502]

Thanks to all for a thread that is both helpful and interesting.

[Michael GilliganParticipant @michaelgilligan61133]

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.

[JasonBModerator @jasonb]

Your Wish………..

[Michael GilliganParticipant @michaelgilligan61133]

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

MichaelG.

[duncan webster 1Participant @duncanwebster1]

2 along and 1 up gives an angle of 26.57 degrees which is fairly close to half of 55 degrees. You’re on your own for 47.5

[Nigel Graham 2Participant @nigelgraham2]

Martin –

Did you succeed in making new Löwenherz thread screws?

[Martin ConnellyParticipant @martinconnelly55370]

Having found the details in Machinery’s Handbook I ground a suitable HSS tool and made two to replace the graunched ones. Simple slotted cheese heads and about 50mm long. Another two originals were undamaged. The music boxes he fixes are tabletop to cabinet sizes. This picture shows a similar one, you can see the two front screw in the raised bosses and there are two in the back.

Martin C

[old martParticipant @oldmart]

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.

[Author]

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