(bicycle) thread identification?

[SillyOldDufferModerator @sillyoldduffer]

Thinking about nuts and bolts it pays to think about what they are for! Many fasteners just have to hold two parts together. For these applications anything that doesn't fall apart will do! The quick repair on my garden gate was structural, but doesn't need to be strong and there's no vibration so I used DIY store M8, galvanised, for cheapness and corrosion resistance.

Quite a lot of manufacturing is like my garden gate; non-critical, where assembly speed matters far more than strength, thus crudely made 4.6 grade fasteners, self-tappers and plastic clips abound. These are good enough because the safety factor is almost zero. Looking inside a washing machine though soon reveals higher grade fasteners where strength, and vibration or fatigue resistance are important. 8.8 Grade fasteners are common on motor mounts and the like.

Conversely, the designer of a safety critical application takes enormous care when specifying fasteners. His fasteners will be made of stronger material, and made to close tolerances for a tight accurately engineered fit. Tight fitting threads are stronger than sloppy threads and much less likely to vibrate loose. Then strength is maximised by torquing nuts to tension the threads 'just-so'. No bodging allowed!

During WW2, considerable difficulties were encountered cooperating with US forces because simple fasteners didn't fit. Tanks, artillery, radar, vehicles and other vital equipment became ineffective waiting for basic spares to turn up, because close allies were operating incompatible thread systems. The Unified System was agreed to alleviate this problem; ideally the alliance used the same threads throughout, but if necessary in an emergency, the match would be close enough for a temporary fix. But it was never intended Unified and Whitworth be interchangeable in critical applications. Bodge allowed to get a tank back into action urgently, not a permanent repair!

This subtlety was lost is translation. In my workshop 'must be OK if it fits' is generally good enough, even though I should know better! Not really a problem because so little of what I do is safety critical. However, mixing Unified and Whitworth is dangerous on parts like motorbike brakes, where coming apart could be fatal. As always safety is about engaging brain.

Another example; cut threads are forbidden in safety critical applications because they are only about half as strong as rolled-threads in the same material. That a lathe made thread was produced by a master-craftsman counts for nothing: rolled threads are always stronger!

Dave

[Howard LewisParticipant @howardlewis46836]

Michael,

No, It was on a bus company. His decision just made a lot of work and complication for everyone lower down the chain of command. (He probably thought that it saved on stocks of spare hardware Taps and Dies ).

Having worked, until then, with Unified and metric, as well as Whit form. It just seemed perverse to me.

What vehicle manufacturers did, or his Engineers thought, seemed to be of no consequence to him.

Takes all sorts

I try not to use "non prototype" threads when working on , but one of my later creations, purely for personal use incorporates a 4 mm pitch thread of sorts, as well as a Whitworth! (So not really practicing what I preach )

Howard

Edited By Howard Lewis on 11/04/2021 13:38:17

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 11/04/2021 13:37:32:

Michael,

No, It was on a bus company. His decision just made a lot of work and complication for everyone lower down the chain of command. […]

.

Thanks for the clarification, Howard

MichaelG.

[Oily RagParticipant @oilyrag]

Posted by jon hill 3 on 09/04/2021 23:02:41:

Thanks for all the help everyone! Note to Nigel my Whitworth thread gauge seemed to fit hence mistaken for such.

Again a book or website recommendation on threads going into pitch, tpi, history etc would be very helpful.

If you want the 'works' when it comes to threads there is only one book in my estimation:-

"Guide to World Screw Threads" by P.A. Sidders ISBN 0-89381-1092-9 Published by 'Industrial Press Inc.'

Get to count how many metric thread variations there are for 6mm for instance (Answer = 26!) and so the wonderful observation by one wit that "the beauty of metrication is that everyone can have there own standard".

As for the argument about shuffling imperial BSW and UNC nuts and bolts there is an anecdote about a Formula 1 engine that repeatedly, after about 300km distance, would have the main bearing web buttresses within the cylinder block fail. This was traced to the M11 (yes! M11 – because M10 was too small and M12 took up another 6mm of engine length) main bearing studs. The options were either to bite the bullet and make the block 6mm longer and change to M12, or make the M11 work. It was pointed out that maybe the M11 should be designated as a MJ11 (MJ being the aerospace metric equivalent with Whitworth type crest and root form) but as this was a 'bastard' thread (non standard!) the tooling would take 9 months and a tap was going to cost in excess of £250 each. The answer? …… Make the MBS's 7/16th Whitworth! (virtually 11mm) with the added advantage of the stronger 55 flank angle as against the 60 degree angle of the metric thread. Never had another failure after the change to 7/16th Whit.

Martin

[CHAS LIPSCOMBEParticipant @chaslipscombe64795]

A really interesting set of replies and very helpful. as usual Hopper and S.O.D have come up with common sense answers. Clearly it really doesn't matter a hoot for the miscellaneous small fittings on motorcycles which is what I had in mind. If the application was more demanding e.g. timing shaft nut to secure the timing pinion, then I would be sure to use matching thread forms, just as a precaution.

I really wonder just how accurate thread angles would be on el-cheapo handyman screws from Thailand or China would be anyway?

Chas

[Neil WyattModerator @neilwyatt]

Camera tripod threads are deliberately made sloppy so that you can use either BSW or UNC.

The original standards were 1/4" and 3/8" BSW , but these days it is technically UNC for photo tripods.

In most of the world (outside the USA) 1/4" and 3/8" BSW are the standard for microphone stands.

Cameras you are usually OK, but I have had nominally matching microphone stand/adaptor/holder threads that are just too tight to do up correctly or comically (annoyingly) loose, apparently at random.

Neil

[Swarf MakerParticipant @swarfmaker85383]

Poor Mr Whitworth must be positively squirming in his grave.

[Nigel Graham 2Participant @nigelgraham2]

I have beside me one of my Tracy Tools charts. (The other is hanging up in the workshop.)

Looking at some of the odder-looking metric pitches listed above, it seems they might not be the "specials" they seem. It's possible some exist to suit particular trades.

'

The racing-car engine could have M11 threads if the rest of its fastenings are metric.

By comparison, the pitch of the close-to-11mm, 7/16 X 14 tpi BSW is 1.81mm. (BSF is 0.71mm pitch).

There are four ISO-Metric M11s: 1.5mm pitch Coarse, and 0.75, 1.00 and 1.25mm, Fines.

.

Howard's 4mm pitch finds itself in the standard ranges as M36 and M39 Coarse, and M52 fine – all still ISO-Metric – but obviously there is no reason we can't use non-standard pitches for special applications to our own designs.

'

A risk with mixing standards that sort of fit together is that of distorting the threads unduly by unfairly concentrated loads, so best avoided in anything critical, or where there may be a risk of the nuts swapping around with each other.

Bolting garden-gates together, or something equally unlikely to fall apart, is a different matter, and though I'm sure we do all try to be consistent, as Chas points out, we would not really expect the El Cheapo building-site fastenings being any better than they should be. Nevertheless, if my workshop's travelling-hoist collapsed I would blame my design, workmanship or over-loading, not its fastenings, all ISO-Metric Coarse, even though they are all just ordinary nuts and bolts from the builders' merchants.

Often, the bigger threat to the joint's safety is not the nut on the bolt but the nut putting the nut on – by carelessness, thoughtlessness, tiredness, pressure to finish the work, etc. One of my old text-books, written before torque-wrenches, states that spanner lengths had become developed with respect to the torque exerted by them by the average fitter. So joints would be designed for the strengths necessary for their own duties, including the bolt diameters; but the spanners were sized to minimise the risk of the fitter breaking the bolts in normal use. Perhaps it was taken that he had sufficient skill to judge appropriate tightness and insufficient strength to snap the screw!

[I have once had to tighten a screw and nut until the former sheared! The M5 cap-screw and 'Nyloc' nut, both in stainless-steel, were in two rings holding together a two-part annular rubber housing, and one of the inner-ring pairs galled while still loose. As it was down inside a cylindrical cavity, inaccessible to any other tools, shearing the screw was the only option.]

[Dr. MC BlackParticipant @dr-mcblack73214]

Posted by Swarf Maker on 12/04/2021 00:15:52:

Poor Mr Whitworth must be positively squirming in his grave.

Sir Joseph Whitworth !

If you are interested ………….

Sir Joseph Whitworth, 1st Baronet FRS FRSA (21 December 1803 – 22 January 1887) was an English engineer, entrepreneur, inventor and philanthropist. In 1841, he devised the British Standard Whitworth system, which created an accepted standard for screw threads. Whitworth was created a baronet by Queen Victoria in 1869. Upon his death in 1887, Whitworth bequeathed much of his fortune for the people of Manchester, with the Whitworth Art Gallery and Christie Hospital partly funded by Whitworth's money. Whitworth Street and Whitworth Hall in Manchester are named in his honour. (copied from Wikipedia)

[HopperParticipant @hopper]

Posted by CHAS LIPSCOMBE on 11/04/2021 23:28:44:

A really interesting set of replies and very helpful. as usual Hopper and S.O.D have come up with common sense answers. Clearly it really doesn't matter a hoot for the miscellaneous small fittings on motorcycles which is what I had in mind. If the application was more demanding e.g. timing shaft nut to secure the timing pinion, then I would be sure to use matching thread forms, just as a precaution.

I really wonder just how accurate thread angles would be on el-cheapo handyman screws from Thailand or China would be anyway?

Chas

Not very.And distort the first time they are tightened up.

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