Hubcentric rings are used in aftermarket wheels to center the wheel ono the hub when the hole bored into the wheel is not exactly the same as the vehicle hub.
Aftermarket heel manufacturers will make the bore of their aftermarket wheels the largest size to suit the largest hub size of the vehicle that same bolt pattern, and then use hubcentric rings to resize the wheels to suit all the cars with consequently samller hub diameters.
This ensure that the wheel is centered and thus the studs aren't flxed (which causes them to eventually snap). The studs are there ONLY to provide a clamp force - NOT to carry the load of the car. The clamp force induces a friction force between the wheel and the hub/rotor and THAT is what carries the load.
Without the rings you will NEVER get the wheel prperly centered this flexes the studs and also over signifigant bumps the wheels can slip and go off center even more, cause more stress on the studs and possible instantaneous failure.
To check if you need rings on your aftermarket wheels (which most do), unbolt your wheel bolts and observe the wheel. While pressed flat against the hub, does the wheel rest on the studs? If so then you need the rings. Elky, IIRC you have FSVT wheels - those I doubt need rings as they are machined especially for Ford and thus have the hub hole in the wheel machined to the required 63.4mm diameter.
