The park tool bbt 49 bottom bracket tool is a 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 49 bottom bracket tool features the bbt 49 is a precision machined aluminium tool for the installation and removal of 16 notch external bearing bottom brackets with an outside diameter of 39 mm the bbt 49