WHEEL HUB DIMENSIONS (mm)
Note 1. The wheel type designation refers to the maximum size of outer bearing, in millimetres, which can be used with that hub.
Note 2. Actual hub diameter is measured across the outside of the splines on the car and not the wheel itself.
Rudge fine spline 52mm
Rolls Royce RAF spline wheel centre
In Europe most hubs are of the Rudge-Whitworth type with V-shaped splines with dimensions as above.
On Rolls-Royces, and in America, you may find RAF type hubs which have square splines.