CarloSW2,
OK, I can see that as an alternate explanation for the Moon Craft arrangement.
Of course, you can't really tell whether the center part, the "donut hole"
comes off first, or the cover, I guess that's the "donut," does. Maybe you
just push on the "hole," and the "donut" comes off.
It seems like the air valve access hole is somewhat larger than necessary to
get an air hose pressed on. Maybe it needs to be that big to get your fingers
around the valve cap.
It's too bad that there isn't more info readily available on these covers.
They have only appeared on a few cars.
I would
really, really like to know more about them... $$$
