Birzman B.B. Socket Bottom Bracket Tool Description: The Birzman B.B. Socket Bottom Bracket Tool works with Shimano Hollowtech II external bottom bracket cups featuring 16-nothces and other similar external bottom bracket assemblies with a 44mm cup diameter. Features: Bottom Bracket cup tool intended for use with 1/2" socket drive wrenches Addresses external bottom bracket cups or external threaded lockrings on Centerlock rotors Also fits Shimano BB Tool Adaptors TL-FC24 & TL-FC25 Specifications: Material: Hardened Steel