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Old 10-22-09, 12:33 PM   #1
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Threads Fit or not?

Hi all,

Having some issues with threads.

I understand from (Barnett Manual) that threads used on bicycles can be one of these standards:
  • ISO ((International Standards Organization)
  • BSC (British Standard Cycle)
  • Italian Whitworth
  • Whitworth
But I'm really confused on what this means..... are some of these like Italian Whitworth only for a brief period
of time in a faraway place and not of consequence - or do these actually show up occasionally?

Are all new machines built only with, maybe, ISO or BSC or Metric?

and if ISO is Metric (exclusively?) then ISO and Metric must(???) somewhat (or entirely?) overlap. Or is there
something else to know about.

None of this is entirely clear from reading.....
Also, there are Fine and Course threads - are Course threads every found on bicycles?
also of course there are many major diameters but I can't think where really big or really small ones might be used
on a bicycle. Is there a chance somebody might be able to give me a practical range of what major diameters a
shop should stock?

Finally to Know something is compatible from specs I'm thinking we'd have to know all these things:
  • Male/Female
  • Hand
  • Fine/Course?
  • Standard
  • Major Diameter

are there maybe other things to know before we can be sure that the two parts are going to be mate perfectly?
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Old 10-22-09, 12:38 PM   #2
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"ISO" is neither English or metric, but a curious amalgam of both. Most fasteners used on bicycles are metric (M5 x 0.8 and M6 x 1.0 are probably the most common). Most modern bikes will be built to ISO specifications.
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Old 10-22-09, 01:09 PM   #3
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Unless you're dealing with really old bikes, threads are no big deal. You've got the standard English and Italian BB threads, the RD mounting thread, which is normally 10mm x 1mm and water bottle threads that are 5mm x .8mm. The cable guide under the BB should have the same thread as the water bottle mounts.

A removable RD hanger will use standard M4 or M5 bolts.
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Old 10-22-09, 03:09 PM   #4
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Bicycles typically use standard metric fasteners with M5x.8 and M6x 1.0 being the most common. The M5x.8 nomenclature means a metric bolt 5 mm in outside diameter with a thread pitch of 0.8 mm. Other metric fasteners follow this convention.

Bottom brackets are most commonly "English" threaded which has been accepted as the ISO standard too. The threads are 1.37" diameter by 24 threads per inch. The drive side cup is left-hand (reverse from normal) threaded. The non-drive side cup has common right hand threads.

Italian bottom brackets are 36 mm in diameter x 24 threads per inch or a bastardized English/Metric standard. Both cups have common right hand threads

Rear derailleur hangar threads are M10x1.0 which is a much finer thread pitch than commonly found on 10 mm bolts.

To go into the detail you are asking about, a current machinist Handbook is probably a good investment.
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Old 10-22-09, 03:11 PM   #5
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Most rear axles are 10mm by1mm thread pitch. The fronts are 9mmX1mm. Sometimes you will find 26threads per inch, but not often.
Pedals on most bikes are 9/16"X20TPI. Some are 1/2"X20TPI.
Female parts are like nuts and the bolts are the male parts.
Radial (cartridge) bearings are for the most part metric and have a simple numbering system. My Phil bottom brackets take a 6907 2RS bearing. The ID is 17mm, the OD is 30mm and the width is 7mm. The 2RS signifies 2 rubber (dust) seals.
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Old 10-22-09, 05:36 PM   #6
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Many thanks!

This has been a big help and also a big relief - seems that on the practical side there are special threads for BB, Pedals, and RD plus a few more - but otherwise M4, M5X0.8, M6 (x 1) and a few more should cover it.

Btw I checked on the English Trike (ICE) at a regional shop here - that I have been day-dreaming about - and the mechanic said something like "they are all using metric nowadays (meaning, I guess English trikes)".

This raises the backwards question - who isn't playing along with the metric standards (except for the hand-me-down "special" standards such for the BB)?


My best thought now is to present a quick list of the popular sizes such as above first with "Other"
and if response is "Other" then give a complete set of params specific to each component (eg L/R for BB and PD). That'll keep it simple most of the time but allow flexibility when it is needed for oddballs or really old.

Thanks again,

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