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I bought a SunRace bottom bracket (BBS18). It didn't come with crank bolts, but since all the other crank bolts and bottom bracket I've used have been compatible with each other, including with other new cartridge-style bottom brackets, I expected that this would be compatible with the bolts I already have.

It isn't.

The crank bolts I do have went in a few turns, then the threads bound. I can force it, but this will start to damage the threads. They clearly have a different thread specification.

What different specifications exist? (And what bolts should I look for in this particular case? It's a M8 x P1.0 thread; how are these bolts likely to be described by cycle component retailers?)

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SunRace spec sheets show the crank bolts should be M8x1.0. The bolt diameter is 8mm and there is 1mm betwween thread peaks. This size is by far the most common. However there are other standards. Truvativ seems to have the most variations using M8, M12, M15 plus some self extracting bolts. If the bolts starts but binds it is likely the right diameter but the wrong thread pitch (most likely M8x1.25).

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  • The other bottom brackets I have are Shimano and (I think) Stronglight; they were compatible with each other.
    – Daniele Procida
    May 9, 2020 at 21:40
  • The BB threads are probably not formed well. It's trying to be 8x1 for sure.
    – Nathan Knutson
    May 9, 2020 at 22:01
  • @NathanKnutson: Or those bolts have issues. OP should try any other M8 at hand to check the threads. If they don't fit either, the issue lies with the spindle.
    – Carel
    May 10, 2020 at 19:12

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