Tom Martin wrote:
>Sheldon Brown to the rescue:
>
> Freewheel Threading
>Type Thread Specification Equivalent
>I.S.O. 1.375" x 24 tpi 34.92 x 1.048 mm
>British 1.370" x 24 tpi 34.80 x 1.058 mm
>French 34.7 x 1 mm 1.366" x 25.4 tpi
>Italian 35 mm x 24 tpi 1.378" x 1.058 mm
>Metric BMX 30 mm x 1 mm 1.181" x 25.4 tpi
>
>French and Metric BMX freewheels thread don't work with anything else.
>ISO, English and Italian are all semi-interchangeable, but it you
>shouldn't go back and forth between different types of freewheels on the
>same hub repeatedly.
>
>There are subtle differences between BSA and ISO threads. There is also
>a difference in the pitch of the threads (one is 60 degrees, the other
>is 45 degrees? Am I right?
Nope, the pitch of both is 24 threads per inch.
The thread angle of both is 60 degrees.
Italian is the oddball in this regard, with a thread angle of 55 degrees (derived from the old British Whitworth system.)
See the Bottom Bracket entry in my Bicycle Glossary for details.
http://sheldonbrown.com/
Basically, you don't need to worry about _freewheel_ threading except with old French stuff, everything else is interchangeable.
Sheldon "FAQ" Brown
+---------------------------------------------+
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