>Anybody know why they differ in the first place and
>why the threading is 1.37 inches for English and 36mm
>for Italian?
I don't know why there are two different standards in widespread use, let alone all the others, but I do have one piece of info that may or may not already be obvious. For some time is wondered where an archane standard like 1.370" came from. When I realized that this is simply 1 3/8" and it suddenly seemed a bit more reasonable. Don't know of many machinists who work in fractions, but maybe back in the day...
What IS whacky is the mixing of, metric and "English" units on Italian thread specs. BBs are 36 millimeters at 24 threads per inch???? (Campy axles and hanger bolts are similarly confused). I think this is because many machine tools can cut an infinite range of diameters, but threading options are restricted by the lead screw pitch.
Tom Dalton
Lehigh Valley, PA
> Does the 70mm for Italian bb shell, vs 68mm for
> English offer any advantages?
> As I was riding today, I was noticing how the
> chainstays fit into the bb
> shell and wondering whether an extra mm width would
> make for a stronger rear
> triangle. Seems like it is too small to make a
> difference to me. Anybody
> know why they differ in the first place and why the
> threading is 1.37 inches
> for English and 36mm for Italian? Lou Deeter,
> Orlando FL. Obviously with
> way too much time on my hands on a Stupor Bowl
> Sunday.
>
>
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