Wheels Manufacturing Narrow Flange BB ToolThin Flange Bottom Bracket Socket Designed to create a tight grip on thin flange bottom bracket to avoid slipping while torquing cups into bike frames. This single sided socket is used for installing and removing 48. 5mm, 16 notch bottom bracket cups. The socket has a machined 3 8'' drive, which can be used to allow 3 8'' drive torque wrenches to be attached and locks onto 1 2 inch UNC press rod for secure and easy installation of thin flanged bottom