It's a spinner. 'nough said.
Center of gravity should be spot on as shown in the image..
I used these ring bearings and ball bearings...
I've printed the version without the ring and it was pretty good, if you don't mind occasionally getting 'kicked' in the fingers by the gymnasts.
On second look, there could be a bridging concern for the one with ring, but probably not. I will improve the design if/when I can get to it.