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Old 10-14-18, 04:24 PM
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JohnDThompson 
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Originally Posted by vailskier3 View Post
Ok, so I just measured my bottom bracket shell and it looks like its 70mm. That means it is italian thread, correct?
Not necessarily. Shell width is only loosely correlated with thread spec. While many Italian road bikes have 70mm wide shells and Italian thread, some Japanese road bikes from the 70s and early 80s have 70mm wide shells and English thread. And some Italian track bikes from the 60s and 70s have 65mm wide shells and Italian thread. And some frames start out with 68mm shells and English thread, then get cross-theaded and stripped so an English thread bottom bracket is not secure, so the frame gets reamed and re-tapped to Italian thread.

The only way to be sure what thread your bottom bracket shell uses is to check it directly. If it's Italian thread, a known English thread cup will fall into the shell without engaging any threads.
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