Need to find and fit a 46/36 chainset to my cx bike. The current one - fsa omega - works with a BB30. Have found others on ebay etc by different companies (the fsa omega version just seems to have disappeared) - but not sure if they would fit my bike. If i did go with another brand (eg shimano rs500) would I then need a different type of bottom bracket? Also is the hole for the bottom bracket a standard size on all bikes? Or do they come in all different specific diameters? PS - just found a shimano rs500 bb. So assuming this goes with the rs500 chainset, my edited question is would the two together fit on my Cannondale CX, which currently has bb30 and fsa chainset?