The Shimano Tiagra BB-RS501 Bottom Bracket with English threaded cups delivers smooth, low-friction performance for 2-piece road chain sets. Featuring a new long-lasting seal design and minimal bearing interface, the BB-RS501 ensures smooth rotation and easy installation. Compatible with Shimano Hollowtech II 24mm spindle chain sets and 68mm English threaded frames. Buy your bike bottom brackets & bike tools at Halfords, the UK's largest bike accessories retailer.