I call them Simulators when the Rear Cover is dished IN like the actual wheel in that position. But the above description is good too. Makes the coach look like it has chrome wheels.
Dicor is the common simulator and those use two nuts on each that just catch the last couple threads sticking out of the actual lug nuts. One of our OP's here got a set of Pacific Duallies and really liked them. I think they required bolting a little adapter plate.
We have Dicor Sims and I have a socket for my 1/2" drive to work the nuts. If you need it I can go out later and get you the socket size for the Dicors on Ford wheels. The little gizmo they furnish is not tough enough to get them tight enough to stay put. Nor to get them off if they rust a little. I use NevrSeez on the threads and a tweak with a real wrench.
I'm a fan of custom valve stems, but I would NEVER attach a Valve Extender Hose to a Wheel Cover/Simulator. If that sim wants to break loose, I want it GONE, not flailing away at the coach till it takes the hose and my air away with it.