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Italian & English BB threading - RH cups identical?(3 posts)

Italian & English BB threading - RH cups identical?BergMann
May 22, 2003 10:11 AM
From Sheldon Brown's website, I've tracked down the threading specs for English/ISO BBs as:
1.375" x 24 t.p.i.
and for Italian as
36mm(1.417") x 24 t.p.i.

What does the first number refer to? External cup diameter? Width of threads on cup?

The basic question is if a right-hand English cup will fit the non-drive side of both an English and Italian threaded frame. (I'm not concerned with shell widths for the moment - the cartridge BB I want to swap doesn't use external lockrings).
No!satanas
May 22, 2003 10:26 AM
1. 1.370" = 34.8mm
2. Italian RH cup has RH thread, English RH cup has LH thread
3. Thread form is different

English cup doesn't engage threads in Italian frame; Italian cup won't go into English frame.

Number is diameter of thread (34.8 versus 36mm).

You'll need a different BB...
Or at least two new cups...BergMann
May 22, 2003 12:40 PM
Thanks for confirming that first number was a diameter dimension.
I'm not sure what you mean by thread "form" but the thread pitch is identical at 24 tpi. Theoretically speaking, if the left cup were 1.2mm bigger in diam., the threads should match identically, shouldn't they?

My goal is to contact the manuf. of my Ti cartridge BB and see if they make an Italian cupset -- I just wanted to know if I had to get both cups or just the drive side.
Thanks for your help sorting it out!