Always confused over threads and tapping

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I've always understood that UNC & UNF only go down to 1/4" generally, which succeeded the NF designation and the ANC & ANF are all below 1/4" but there are Unified screw threads below 1/4" for attachment purposes, one of which is 10 x 24 which is a non preferred size and the tapping drill for that is No. 25 and this thread differs from the ANC one, on the nut core Dia. Depth and Effec.

Regards Nick.

[Tim StevensParticipant @timstevens64731]

If the thread is to be made in cast iron or light alloy a coarse (20 tpi) thread will be stronger than M6 which is 25.4 tpi and a smaller diameter.

And if you can tell the visual difference between a bought-in component with UNC threads, and one with Whitworth, please tell me the details of your optician.

Cheers, Tim

[EmgeeParticipant @emgee]

Tim

One way to note the difference is to try fitting a 1/4" 20 UNC into a 1/4"W tapped hole, it may just locate but not enter the tapped hole because of the angle variation, but yes difficult to see the difference without a thread gauge.

Emgee

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Tim Stevens on 20/02/2022 21:00:18:

[…]

And if you can tell the visual difference between a bought-in component with UNC threads, and one with Whitworth, please tell me the details of your optician.

Cheers, Tim

.

It’s very easy with suitable visual magnification, Tim … [assuming, of course, that you buy your components from someone that actually makes them to spec.] … but I’m sure you know that.

MichaelG.

.

As requested: **LINK**

https://www.moransopticians.co.uk/oct-eye-scan

.

As evidence : This is a wax impression from the lens mounting ring of a Leica camera … which I photographed to demonstrate that the 39mm thread has Whitworth form: 

https://www.model-engineer.co.uk/wp-content/uploads/sites/4/images/member_albums/79913/897301.jpg

The Whitworth profile quite recognisable to the assisted eye.

Edited By Michael Gilligan on 20/02/2022 23:04:16

[Bill PhinnParticipant @billphinn90025]

Michael, I've used these successfully with magnification to distinguish UNC from BSW but I'm usually defeated by sizes below 3/16" unless I sit down with the fastener clamped and use high magnification in very good light.

Can you give any quick tips on what is required to take photos like the one in your post and overlay a 55 degree angle of exactly the right size?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bill Phinn on 20/02/2022 23:31:00:

[…]

Can you give any quick tips on what is required to take photos like the one in your post and overlay a 55 degree angle of exactly the right size?

.

Bill

That particular one was photographed using one ‘channel’ of my stereomicroscope, and the angle was measured using an iOS App called EP Calipers [which is intended for checking ECG traces] … but plenty of hardware/software alternatives are available.

As mentioned, it was a wax impression; which I then roughly sectioned by hand with a razor blade.

The point for Tim’s benefit though is that the Whitworth profile is easy to recognise visually.

Happy to discuss further by message if you wish.

MichaelG.

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Ref. __ **LINK**

https://apps.apple.com/gb/app/ep-calipers/id982313078

[Anonymous]

Posted by Nicholas Farr on 20/02/2022 14:28:14:

Hi, I've always understood that UNC & UNF only go down to 1/4" generally, which succeeded the NF designation and the ANC & ANF are all below 1/4"

That may be what you call them in the UK – and for all I know it may be technically correct – but on this side of the pond they are pretty much universally referred to as UNC/UNF for the whole range.

[HopperParticipant @hopper]

Posted by Emgee on 20/02/2022 22:22:54:

Tim

One way to note the difference is to try fitting a 1/4" 20 UNC into a 1/4"W tapped hole, it may just locate but not enter the tapped hole because of the angle variation, but yes difficult to see the difference without a thread gauge.

Emgee

Absolutely not so.

I screw UNC bolts into BSW tapped holes all the time and have never had one that did not fit. Mass produced nuts and bolts are made to loose tolerances and BSW/UNC fit together just fine as a result, as long as TPI is the same for the diameter. That is why when you screw say a UNC nut onto a UNC bolt, you will feel the nut is free to wriggle about. They are not made to tight enough clearances where both sides of the thread flanks are in contact.

Plenty of space there to accommodate the tiny, tiny difference in flank angle — a whole 2.5 degrees on each flank, over a distance of the thread depth, say 20 to 40 thou. Do the math and the actual dimensional difference is in the tenths of a thou.

We can't even buy BSW bolts or nuts here in Australia anymore. Suppliers just give you UNC in the appropriate size, because they always fit together with BSW. Always. Just a PITA when you have to go get an AF spanner to undo a fastener on an otherwise BS machine. I've been riding British and American motorbikes held together with such mixtures for donkeys years and never had a problem. And all my workshop projects made from scratch are held together with UNC high tensile socket head cap screws that are screwed into BSW tapped holes because that is the only set of coarse taps I own. Never once had a problem.

And also no point in agonising over rounded thread tips vs flat. That is a clearance area of the thread so does not matter if one round and one is flat, they make not contact with each other on mass produced fasteners. Contact is purely on the one thread flank.

[HopperParticipant @hopper]

PS here you go. Brand new 1/4 UNC cap screws screwed straight into the original BSW toolpost holes as tapped by Myford at Beeston in 1957. Never a problem.

And 5/16 UNC cap screws screwed into 5/16 BSW holes I tapped myself with a BSW tap on this four way toolpost I made for the Drummond.

[Gerard O’TooleParticipant @gerardotoole60348]

Posted by Hopper on 20/02/2022 11:24:52:

Posted by br on 20/02/2022 11:16:04:

Posted by noel shelley on 20/02/2022 11:01:11:

Whilst on the subject of threads what is the difference between BSB and BSC both are 26tpi ? does one have a different thread angle ? Noel.

Yes – different thread angle – BSB is 55, BSC is 60. – according to a google search which hopefully is correct ?

bill

 

But once again, the one will screw into the other in most practical instances. T( so wont fit together ) while BSB remains 26TPI throughout.

Edited By Gerard O’Toole on 21/02/2022 08:11:11

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Hopper on 21/02/2022 03:57:26:

Posted by Emgee on 20/02/2022 22:22:54:

[…]

 

Absolutely not so.

I screw UNC bolts into BSW tapped holes all the time and have never had one that did not fit. Mass produced nuts and bolts are made to loose tolerances and BSW/UNC fit together just fine as a result, as long as TPI is the same for the diameter. That is why when you screw say a UNC nut onto a UNC bolt, you will feel the nut is free to wriggle about. They are not made to tight enough clearances where both sides of the thread flanks are in contact.

[…]

.

… and there’s the rub [or lack of it]

“Mass produced nuts and bolts are made to loose tolerances.”

The UNC system allows one to specify the ‘Tolerance Class’

MichaelG.

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Edit: __ A useful illustration of class 3 [which has tighter tolerances] can be found at:

 https://www.newmantools.com/taps/taptech.htm

and I have reproduced here with due credit

Edited By Michael Gilligan on 21/02/2022 08:56:33

[john halfpennyParticipant @johnhalfpenny52803]

In the UK I work with BS threads every day on classic cars from the fifties. We know that, say, 5/16 UNC will screw on or in BSW quite easily, but the combination often locks up horribly when you try to unscrew. Fortunately we can get BS screws and bolts without difficulty, so we don't need to resort to a unified thread bodge, apart from the natural desire to do the job correctly and give the right head/spanner size. Of course, on these cars many bought out parts, from suppliers such as Lucas, are unified threads because the changeover date was not consistent, so care is needed.

[Gerard O’TooleParticipant @gerardotoole60348]

Sorry don't know what happened to my post above

Just wanted to add that BSC and BSB differ on sizes below 1/4" where the Cycle thread has TPI which varies fbetween 32 TPI or 40 TPI while BSB remains 26TPI throughout its' range.

[larry phelan 1Participant @larryphelan1]

Even getting stuff from England to this quaint little land is becoming a no-go.

[HopperParticipant @hopper]

Posted by john halfpenny on 21/02/2022 09:33:03:

In the UK I work with BS threads every day on classic cars from the fifties. We know that, say, 5/16 UNC will screw on or in BSW quite easily, but the combination often locks up horribly when you try to unscrew. Fortunately we can get BS screws and bolts without difficulty, so we don't need to resort to a unified thread bodge, apart from the natural desire to do the job correctly and give the right head/spanner size. Of course, on these cars many bought out parts, from suppliers such as Lucas, are unified threads because the changeover date was not consistent, so care is needed.

I have never experienced that type of lock up in 50 years of mixing the two threads, both at work as a fitter or at home on the motorbikes or shed equipment. Famous last words! I won't be game to do it again now.

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by Peter Greene 🇨🇦 on 21/02/2022 01:45:40:

Posted by Nicholas Farr on 20/02/2022 14:28:14:

Hi, I've always understood that UNC & UNF only go down to 1/4" generally, which succeeded the NF designation and the ANC & ANF are all below 1/4"

That may be what you call them in the UK – and for all I know it may be technically correct – but on this side of the pond they are pretty much universally referred to as UNC/UNF for the whole range.

Hi Peter, thanks for your enlightenment, I guess some publishers in the the UK need to get up to speed. Both Unified Thread Standard and ANS vs. UIS make interesting reading. I don't have up to date Zeus data charts booklet, so don't know if they have made any significant changes to those that I've had for many years.

Regards Nick.

[john halfpennyParticipant @johnhalfpenny52803]

I sympathise Hopper; needs must. It's also true that some suppliers do try to send UNC in place of BSW on the basis that close enough is good enough – and presumably of loose tolerance, or BSW heads on UNC threads (these probably of chinese manufacture)

[HopperParticipant @hopper]

I wish they would send us UNC threads with BS heads! At least you only need the one set of spanners per vehicle then. As it is now, all too often an old bike will have a mixture of BS, AF and metric hexes dotted about it.

But I am guilty of creating my three penn'eth of confusion, making tooling for my Myford I find myself making things like a rear toolpost mounting stud with a 7/16 UNF thread because that is what taps and dies I have, but I machine my own nut for it with BS sized hexagon so it matches the Myford standard spanner set on the wall behind it. Someone in the future will be scratching their head over that one.

[EmgeeParticipant @emgee]

From what Hopper shows in the pics it seems I have to dump my old 1/4" W taps as they must be worn beyond the limits, or buy some low cost UNC screws when needed.

Emgee

[john halfpennyParticipant @johnhalfpenny52803]

Also guilty of that Hopper. My lathe has metric threads, but my mods (dro , carriage stop etc) are attached with bs cap screws because I had them.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Hopper on 21/02/2022 09:53:05:

Posted by john halfpenny on 21/02/2022 09:33:03:

In the UK I work with BS threads every day on classic cars from the fifties. We know that, say, 5/16 UNC will screw on or in BSW quite easily, but the combination often locks up horribly when you try to unscrew. …

I have never experienced that type of lock up in 50 years of mixing the two threads, both at work as a fitter or at home on the motorbikes or shed equipment. Famous last words! I won't be game to do it again now.

Much depends on what the nuts and bolts are for. The penalty of mixing 55° and 60° threads of the same TPI is a reduction in strength, coupled with an increased chance of jambing or coming loose. I couldn't find any comparative numbers, practical or theoretical, quantifying the difference.

Found a couple of convincing examples saying 55° BSW threads perform better in cast iron than 60° threads (UNC or Metric) but it's a special case. For most purposes 60° threads are better than 55°.

As ordinary nuts and bolts are plenty good enough for almost everything I do intermixing BSW and UNC is a useful trick. But I wouldn't do it if the fixing had to be strong or vibration proof. Very unwise to replace the Grade 8.8 high tensile bolts on my Engine Crane with ordinary DIY Store bolts because the latter are at least half as strong and could be much weaker. Strong nuts and bolts are made of higher specified steel with tighter fitting close tolerance threads: it makes a big difference.

Dave

[bernard towersParticipant @bernardtowers37738]

I really have problem with this discussion as some of you are actually looking to mismatch fasteners, why do you think the designers of these fittings made both parts match..I could not in all honesty make stainless or any other material fasteners that did not match. Let’s be fair all the information required for thread sizes /rates /tapping sizes/ clearance/ and ods in the case of numbers is all out there pull it off print and read it.If a jobs worth doing.!!

[Tony Pratt 1Participant @tonypratt1]

Bernard, as you say you have the 'problem', in the real world BSW & UNC will work together with no problem apart from 1/2" diameter. If you are making both obviously match the angles etc etc, otherwise in reality it matters little, an engineer will put accuracy/precision where it's needed.

Tony

[Neil WyattModerator @neilwyatt]

Not sure if it's been mentioned but for camera tripod 1/4" and 3/8" threads the past standard was BSW and the modern one is UNC, but usually they are made 'loose' enough that either is an easy fit.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 21/02/2022 21:05:28:

Not sure if it's been mentioned but for camera tripod 1/4" and 3/8" threads the past standard was BSW and the modern one is UNC, but usually they are made 'loose' enough that either is an easy fit.

Neil

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Not previously mentioned on this thread, Neil … but it’s a good point, and a prime example of the expedient use of the appropriate UNC ‘Tolerance Class’

MichaelG.

[Author]

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