The Shimano BB-MT501 bottom bracket for Hollowtech II provides better sealing and rotation to delivery high driving efficiency. English (BSA) threaded bottom bracket Fits 68 and 73mm frame bottom bracket shells For use with MTB Aluminum threaded cups Item Specifications BB Shell Width (mm): 68 BB Shell Width (mm): 73 BB/Frame Interface: English Bottom Bracket Shell I.D.: 1.37 Defined Color: Black Spindle Interface Type: Shimano Hollowtech II