On one online sales site there's a drop-down widget showing various sizes of the Shimano UN55. "JIS spindle" appears as a bullet-point next to someone of the size choices but not all of them, hence my question:

Is the Shimano UN55 bottom bracket in 68x122.5 and 68x127.5 sizes JIS square taper?

A technical document on the Shimano website didn't resolve my doubts since it doesn't address the spindle standard, and it doesn't mention the 122.5 and 127.5 lengths anywhere, and it shows this BB as available with either English or Italian threads, so who knows if the spindle shape changes too?

Many online vendors include generic pictures with their BB listings and often have incomplete descriptions, so that the inexperienced customer (like me) is often in doubt. For example, I just bought a BB online that had 1.37 stamped on the body in the accompanying picture which turned out not to be 1.37 at all. It had 36mm OD cup thread, not 35mm (1.37).

2 Answers 2


It is JIS.

Shimano doesn't have separate Italian taper cranks, and it does not make sense to them to make BBs that do not fit their other products. Italian taper has been practically obsoleted since Campagnolo switched to two piece cranksets in the 2000s. If you manage to find one now from a competent vendor, it will be clearly marked as one.

Regarding your experience buying online, it does not sound like the vendor did know what they were doing.

  • It's also worth pointing out that they can generally be used interchangeably, as long as you adjust the spindle length to fix the chain line. There would be no reason to do this currently for a JIS crank, but if you had an old Italian crank that you really wanted to use, you could probably get by using it with a JIS bottom bracket. More Info
    – Kibbee
    Commented Mar 27, 2019 at 12:55

On less otherwise stated in the crank literature, all tapered three piece Japanese crank sets are JIS taper. French and Italian crank sets should be matched with the same manufacturer's bottom brackets of the same time line to eliminate any fit issues. I don't advise cross fitting Euro and JIS crank set/bottom brackets as it either wont fit or will deform the crank arm boss. Also, trying to assure the correct chain line is a PITA.

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