(bicycle) thread identification?

I got roped into servicing a friends cycle and along the way of ordering new parts I thought it might be a handy to have a primer on thread identification.

In this instance it was a set of replacement wheel nuts which if my measurements are correct are 9.5mm (3/8" x 26 tpi whitworth. I am aware that there are hundreds of thread types usually identifed by a 3 letter abreviation eg bsf, unf, bsp etc.

Is there a handy reference ie: book, ytube video, website....

Look up Sheldon Brown; it's all there.

Or get Sutherland's manual if you have the money.

Try **LINK**

https://www.engineeringtoolbox.com/british-standard-cycle-thread-d_2041.html

Russell

Edited By Russell Eberhardt on 09/04/2021 11:07:54

Bicycles mostly use Cycle (CEI ) threads which are all 26 tpi, but are NOT Whitworth form.

They are 60 degree. like Unified or Metric threads.

British Standard Brass threads are also 26 tpi, but Whitworth form.

Howard

If the bike is old, the threads are likely to be BSC, but metric has been used for the last 40 years.

Another vote for Sheldon Brown.

B.S. Cycle Threads:

60º included angle. Not Whitworth (55º  ) .

3/8" BSCy - 26TPI - Tapping Drill 8.5mm

Source: Newnes' Complete Engineers' Data Sheets.

Taps and dies are available from, e.g. Tracy Tools.

Edited By Nigel Graham 2 on 09/04/2021 17:38:08

Howard, if I may add some information:

• CEI threads became British Standard Cycle threads when BS811:1950 was published. It is still available from the BSI if you have £186 to burn.
• Although many BSCy threads are 26 tpi, there are others including 24, 32, 40 and more. And left-hand of course.
• Although the thread flank angle is 60°, the actual root and crest profiles are different from Unified and Metric threads.

George B.

Does it make any significant difference in practice (as opposed to theoretical considerations) if a thread is 55 or 60 degrees?

If I mate a 55 degree brass thread nut with a 60 degree CEI bolt, does it really matter?

I'm thinking here of motorcycle type applications, not extreme performance situations.

Chas

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.

CEI = Cycle Engineers Institute

Standardisation; humph! Umpteen different systems, all different in one way or another.

BA = 47.5° flank angle and all different pitches but each dia. related to each other by a constant.

Whitworth group, same flank angle 55 °, some constant pitch like ME 32,40,60TPI BSW, BSF, Pitch varies according to diameter and BSW 1/4"D for example doesn't have same Pitch as 1/4"BSF.

Brass is constant 26t Pitch.

Basically, nothing fits anywhere except within it's own system!

I believe that there is only one exception ; 1/4"dia Brass and BSF are interchangeable.

Trying to use a nut from one system to fit a bolt from another is likely to jam up tight.

Just out of interest the cycle im working one is only 6 yrs old. I am sure it is not the only new-ish cycle using imperial fittings.

I inherited a large number of 26 tpi taps and dies, including some marked LH, from a chum whose late father was a cycle enthusiast many years ago.

If anybody is interested in giving them a good home, please contact me OFF-LIST

MC

Generally speaking, in practice, it is common for 55 degree nuts to be used on 60 degree bolts etc and vice versa by home and professional mechanics. UNC and BSW fasteners have been intermingled for years in Australia with both being available and used, depending on which side of the pond stuff was imported from. Ordinary fasteners and fittings are made to loose enough specs they will screw together and work ok. I've seen plenty of Harleys with BSW nuts and bolts mated to the original UNC fasteners and Myford lathes somehow seem to end up with UNC fasteners coupled to BSW. It works.

But precision threads such as the spindle nose threads and chuck threads on UK made Boxford clones of the US made South Bend lathes seem to be reluctant to fit UN chucks on BS spindles and vice versa, according to various owners in past posts on here.

There is no one resource that will do that for you.

A few steps on your path to screwing utopia:

https://journeymans-workshop.uk/allthread.php

https://www.gewinde-normen.de/en/index.html

https://www.haguefasteners.co.uk/BoltingGuides/HagueFastenersGuideToScrewThreadSizes.pdf

https://www.npl.co.uk/science-technology/dimensional/npl-notes-on-screw-gauges

.

That’s a potential problem with any identification ... You can be easily misled when the pitch matches.

A good thread gauge should match the thread profile very closely, and at 26tpi I would need to use optical magnification to be confident of a match.

MichaelG.

Tubal Cain's "Model Engineer's Handbook" is good reference, on many subjects,.

Section 4 deals with many of the threads of that you are likely to come across

There will be specials with non standard pitches for the thread size, as found on Mandrel noses, but the data on standard pitches, depths, forms, etc can be read across to the non standard sizes.

You may even meet some real hybrids with Imperial pitches on a Metric diameter, or vice versa.

Took a long while to work out that one Metric lathe had a 2 1/4 x 8 tpi Whit form Mandrel thread!

Howard

I was wryly amused by those revelations of so-called "professional " mechanics using fastenings from one series on near-fits from others; but glad I don't use their garages.

If I pay to have my vehicle serviced professionally, I damn' well do not to be later driving up the M6 at 70mph in a ton of steel held together with any rough old nuts that vaguely wobbled their ways along the studs!

Mis-matched threads are not mating by flank area, but by very thin lines - what other short-cuts has the "professional " taken?.

Bad practice does not become good by being common.

'

Come on, we're not those can't-be-bothered-mechanics. We like to think of ourselves as model-engineers who do our best to get it right.

A Cycle Thread is NOT Whitworth!

As in the oldest profession ...

Professional means “does it for money”

MichaelG.

It is all very well being pedantic and saying that a 55 deg nut cannot/must not be mated to a 60deg bolt, but you are talking about a couple of thou fitting difference and load being on a line contact rather than a full face. Does any one have data on how much less load a thread angle miss match can carry?

But I agree, in principle, cut the right thread angle and do things properly. Does it matter for strength? we need to see some data.