From the Tech Library...
"Wheel Spacers / Adapters:
Wheel spacers can be purchased to the wheel out farther. They can also be purchased to adapt an axle to accept a different wheel bolt pattern. They are used by people to space wheels out away from the vehicle if they are swapping rims that don't have the proper back spacing. Sometimes enthusiasts use a spacer when swapping Mustang rims on to their 2WD Ranger to allow enough space for the front center cap to snap on to the wheel.
The adapters are generally used when people swap in an axle that has a wheel bolt pattern different than the other axle on the vehicle. Adding adapters to one of these axles will allow the vehicle to use wheels that can be mounted on either axle.
The spacers/adapters mount by bolting on to the hub where the original wheel studs are and have new wheel studs in the spacer/adapter."
Maybe it helps you, if not, I have no clue, I just passed along this when I was looking myself and thought I'd bring it to your attention.