Hi, I'm hoping to change my BB to that of an old style square tapered BB. The reason for this is that the chainset I've chosen is a square tapered style

I'm hoping this is a common and easy thing to do. My bike is a boardman comp aluminium frame with carbon forks.

I am looking to transform the whole bike into a vintage looking fixie. I'm content with the other parts. I'm just struggling to identify what length BB I will need.

any help greatly appreciated