To accurately identify the BB shell in your frame, it is important that you remove the cranks and bottom bracket from the frame and measure. A few manufacturers Cannondale, Cervelo are using asymetrical BB shells which may require a very specific bottom bracket. Our Bottom Bracket Standards page will help you identify what Bottom Bracket shell your frame has from your measurements. See our Crankset Page for help identifying your crankset.
How to Select a Bottom Bracket - Bicycle Parts Direct
These spindles are getting harder and harder to find. In many cases, it makes more sense to upgrade to an inexpensive modern cartridge bottom bracket. Shimano cartridge bottom brackets are typically coded with a model designation and two numbers: shell width and length. The wider ridges of an Octalink V2 spindle plow into the grooves in an Octalink V1 crank.