This is a Lightweight, CNC bottom bracket is a great replacement for your external 24mm axle type chain sets. â¢68mm/73mm BB shell (BSA)â¢Forged, CNC Cupsâ¢Fits Most 24 Cranksets (Shimano/ Raceface types)â¢High quality sealed bearingsâ¢Lightweight plastic central dirt seal.â¢Black anodised