Wire wheel hob?

[Pat K]

I have a 1985 Avanti with wire wheels.  I was going to get the front tires balanced and the tech said "how do I get that Avanti cap off"?  Damned if I know.  It twists but doesn't seem to be threaded.  Don't want to take a crow bar to it.  Does it just pop off or is there a trick

[arkus]

almost has to have a lock of some kind in from the back of the center piece.