rob:
these adaptor plates dont need a change of hubs, they are simply spacers which bolt onto the face of the hub, the only difference is that the side that bolts onto the hub is the right fittment for the car, while the side that the wheel bolts onto is different, in order to fit wheels from other marques to your car.
example being the 4x100 vw - 5x130 porsche adaptors.
if u were to look at the two side of the adaptor they would be different, one would have 4 holes 100mm apart, which the other side would have 5 holes 130mm apart. thats why they need to be at least 25mm thick, so there is enough space for the wheel both threads to take hold.
HTH
mase