"Sheldon Brown" <
[email protected]> wrote in message
news:[email protected]...
> Mike Shaw asked:
>
> > Any educated guesses from the peanut gallery as to why different BB threadings came into
> > existence? (See the thread on threaded v.
threadless
> > headsets to see more of the discussion.)
>
> That's easy. Bicycles were made first, then came standardization. Originally, each major
> manufacturer had its own proprietary "standards" and then gradually they sorted themselves out by
> an evolutionary process.
>
My big follow on question is how'd they figure out the proprietary systems in the first place? That
the size tubing/parts they happen to have laying around?
> The overall winner was the standard system developed by B.S.A. (Birmingham Small Arms) in the
> early part of the last century. These standards were adopted by the British industry as B.S.C.
> (British Standard Cycle) standards, and since then, with minor tweaks they have become the
> international ISO standards used by most of the industry today.
>
> The value of a left-threaded fixed cup was known a _long_ time ago, but not everybody thought it
> was worth the trouble and expense.
>
> I've also heard it asserted that it is easier to have the threads on both sides of the bottom
> bracket perfectly aligned and concentric if they're tapped in a single continuous operation
> through from one side of the bottom bracket to the other...but I've never seen an Italian or
> French bottom bracket that showed any sign of actually being produced that way.
>
IIRC, I have, but I don't remember what bike it was on. Its been awhile, and I may be mistaken, but
I seem to recall not being able to get the bb cup out the "right" way and had to go the whole way
through the bb. Remember, I'm admitting that my memory may not be right here, so no flames.
> English standards were naturally built to round-ish inch values, basically 1 3/8" x 24 threads per
> inch (or 26 threads per inch for the Raleigh proprietary size.)
>
When you say round-ish, what's that mean?
> European manufacturers naturally used roundish metric dimensions, i.e. 35 mm for French and Swiss,
> 36 mm for Italian.
>
> The Italian threads are the most peculiar of all. They mix units, using metric diameter with
> inch-based thread pitch (24 threads per inch.)
>
> I have heard that this was due to the Italians buying their lathes from England, lathes that had
> back gears for cutting inch based thread pitches only.
>
> Italian threads are also cut with a 55 degree tool, rather than the 60 degree thread angle used on
> metric and American threads. This harks back to the obsolete English Whitworth thread pattern
> (Whitworth was actually the first systematic system of standard threading and wrench sizes.) See:
>
http://sheldonbrown.com/gloss_w.html#whitworth
>
> French and Swiss use 1 mm thread pitch. Swiss is the same as French except for the use of left
> threading on the right side.
>
> Over time, as the bicycle industry has grown more international and parts production has become
> specialized, there has been a strong trend away from the old national based and proprietary
> standards, and toward an acceptance of the international ISO standards. The old national standards
> have become extinct, except for Italian, which is still just barely keeping afloat.
>
> Sheldon "Actually Appeared In Howdy Doody's Peanut Gallery, Circa 1952" Brown
> +--------------------------------------------------------+
> | As far as the laws of mathematics refer to reality, | they are not certain; and as far as they
> | are certain, | they do not refer to reality. --Albert Einstein |
> +--------------------------------------------------------+ Harris Cyclery, West Newton,
> Massachusetts Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com Hard-to-find parts
> shipped Worldwide
http://captainbike.com http://sheldonbrown.com
