I have an old Bianchi Limited road bike converted to a fixed gear. I think it was still using the orignal bottom bracket up until today when I was powering up a hill and all of a sudden the bottom brack just snapped and then popped out.

Anyway now I need to get a new bottom bracket. How do I know what type an size I need to get? I have a formula rear flip flop hub and 126mm spaced droupouts. Any help?