To ensure a smooth rotation that lasts ride after ride, FSA has included stainless steel ball bearings, which sit inside hardened steel races. This ensures this adapting bottom bracket operates efficiently and extends its lifespan. Tech Tip: If you are unsure whether to select the 68mm or the 73mm size, measure underneath your frames bottom bracket shell. Most road bike's BB30 shells are 68mm wide and most mountain bike's BB30 shells are 73mm wide.