Perhaps the first concern is to be convinced that a separate shaft and hub are required. It is possible for a shaft and hub (gear) to be manufactured from one piece. It is not often cost effective to machine from solid bar, but upset forging gives good strength due in part to surface compressive stresses and low stress concentration effects and can be more economical, particularly in large quantities. Major draw backs of these methods and methods of permanent fixing, such as welding of the hub onto the shaft, are that should the hub's assembly wear the shaft must also be replaced. The permanent fixings are rarely available from manufacturers catalogues and so fall outside the scope of this Guide.
For separate units the connection between hub and shaft is often used for overload protection with, for example, a key shearing and allowing the hub and shaft to rotate freely. This is not possible with a composite hub and shaft.