Here's why I asked the question. It's always bugged me that my hubcaps were left unpainted, but had blue overspray on them from a poor/non-existent masking job at the factory. So I picked up some new ones that weren't all beat up, primed and painted them. And what the heck - might as well do the prop wrench too, 'cause it rusts constantly. Besides, who has a prop wrench that matches their boat?
The problem is, now there's no way to put them on without tearing up the paint.
Problem solved: I knew that 8/4 hard maple cutoff would come in handy for something.
The block only contacts the flange, and will leave the paint on the rest of the cap unblemished.
OK, altogether now: "MIKE, GET A LIFE!"
I thought about getting out the airbrush and painting some spirals on them, but didn't want anyone to make fun of me. Good thing that isn't happening. 
