Hello all,

I have an odd sized bottom bracket and i cant seem to find any compatible replacements for it, the bottom bracket measures 68mm width with a 40mm outer diameter. Can some please let me know if they have any idea which standard this is and recommend a replacement that will fit in this bottom bracket. The bike is a limited edition Stealth Thunder if that at all helps

Thank you very much for reading

Neil Cooper

Are you describing the bottom bracket itself or the frame's bottom bracket shell? If you are describing the shell, the OD isn't important but the diameter of the opening, and whether it's threaded inside or not are the needed descriptions.

Thanks "HillRider",

I am talking about the bracket shell sizing, that is 40mm x 68mm. Its internally threaded on either side. It measures roughly 33mm inner diameter and 68mm width with English treads.

wont let me upload a picture for some reason to show you

Thank you for replying

Right okay in case anyone else comes into this issue here is what you need to know .

Thanks to HillRider for pointing out that i was measuring this incorrectly, using the correct measurements i was able to source a replacement and also discovered the correct standard for this is (BB-UN55).

Thanks again man really helped me there had been looking for over a week using the incorrect sizes haha

Neil Cooper

BB-UN55 is not a bottom bracket standard, it is a model of bottom bracket made by Shimano. Apart from finding a model of bottom bracket that fits, you also have to determine the correct spindle length for the crank that you are using and as well make sure to order that bottom bracket in the correct thread standard, it might be sold in both English and Italian threading. There are many types of bottom brackets that will fir your frame. Normally, you have to make which type you need for the crank you will be using

68mm shell width and 40mm OD is entirely typical for bottom bracket shells. You say you already know it has English thread. If you're trying to find the correct spindle length that will depend on the specific crank you intend to mount.