The Shimano BB-UN100 68/122.5 bottom bracket that came with my 2018 Giant Roam 2 feels rough and creaks.

Searching the web, it is hard to find new BB-UN100 brackets. I would like to upgrade to a better bracket.

I see a variety of Shimano UN300 68/122.5 brackets available online. But it is not clear to me what the difference is among the different versions of this bracket.


What else should I be looking for to determine which version of UN300 would work with my bike?

  • Make sure you get the matching shell type (in your case bsa threaded?), shell width (in your case 68mm?) and spindle length (in your case 122.5mm?) and it should fit. I think UN300 is a slightly higher spec, but otherwise identical Commented May 21, 2023 at 17:09

1 Answer 1


With Shimano square taper bottom brackets, the things to look for are the size of shell (68 or 73mm) and the axle length (In this case 122.5). A third important parameter is the threading size and pitch. Your bike has a BSA threaded BB shell (1.37 inches diameter x 24 threads per inch) and requires a bottom bracket of the BSA threaded standard.

Here's Shimano's current line up of square taper spindle bottom brackets. Note the three versions of BB-UN300 with either 122mm or 123mm spindle. Two of the three model numbers are followed by a letter. The letter K denotes the bottom bracket that should be used if the crankset is used with a Chaincase. If your bike has an "E-type" front derailleur, which is one that attaches to a plate that is secured by the bottom bracket cup, there is a BB-UN300-E for that purpose. If neither is true for your bike, then select the BB-UN30O without a trailing letter.

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