The park tool bbt 79 bottom bracket tool is a precision cnc machined aluminum tool for the installation and removal of 12 notch external bearing bottom brackets anodized for easy identification and featuring a ratchettorque wrench compatible 38 drive park tool bbt 79 bottom bracket tool features the bbt 79 is a precision machined aluminium tool for the installation and removal of 12 notch external bearing bottom brackets with an outside diameter of 46 mm the bbt 79 f