I'd be thinking a long the lines of a wheel bearing. might stick out a bit , maybe one of the newer style sealed bearing that doesn't have such a spindle to it. my mind sees that bearing shower when the "wrong(right)" person does the moving of the painting. I guess I know how I was when I was a youngster. there would be that certain someone who will want to see it spin. let me think some more. mounting it to the art and wall will be the real "exciting" part.