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  • The bb shell width varies between the frames because ITA is 70mm wide and BSA is, even more confusingly, 68mm for road and some MTBs but 73 for most MTBs. I would have thought that you should choose the spindle length from the old bike, eg. if the octalink was 121mm on the USA frame, get the same spindle length but with the BB shell to fit the new frame. But, in my experience spindle length is a bit more approximate, especially for geared bikes (as opposed to fixed / single speed where chain line is more critical). So you would get away with a few mm either way, as long as the spindle is long enough for the crank to be clear of the frame on either side. I have in the past bought several BBs with different spindle lengths at the same time and chosen the right one by trial and error, which is annoying but avoids the situation where the one you order is wrong and you then have to wait another few days for the next one to arrive!

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