Pokeball spinner for small hands (624Z bearing)

My son wanted to have the Pokeball spinner (https://www.thingiverse.com/thing:2278247), but he's only 6 and a 608Z bearing-based spinner is too large for his hands. I tried scaling the Pokeball spinner down for a 624Z bearing but it's not a linear scale so it wasn't going to look right.

I therefore redrew the design in FreeCAD using a scaled copy of the Pokeball spinner as a guide.

Be aware that this is *very* small. The centre buttons on the balls are less than 4mm across, so you need