The park tool bbt 59 bottom bracket tool is precision cnc machined aluminum tool for the installation and removal of 16 notch external bearing bottom brackets anodized for easy identification and featuring a ratchettorque wrench compatible 38 drive park tool bbt 59 bottom bracket tool features the bbt 59 is a precision machined aluminium tool for the installation and removal of 16 notch external bearing bottom brackets with an outside diameter of 41 mm the bbt 59 fit