Assorted gemstone donuts or pi stones are great to use to support your favorite spheres! I have them available in assorted sizes below in the drop-down box. A fabulous alternative to plastic, glass or wood sphere stands :)
I tried all sizes of spheres with all the donuts and depending on the weight of the sphere and if it is "perfectly" round (which they are not) you may want to go a size bigger, rather than smaller. But I was able to place 30 to 50mm spheres on the small, medium and large pi stones and they didn't roll. A very large sphere should go on an extra large, or xx-large donut. I will be getting more in shortly.
The measurements are approximate and each stone is different as these are all unique.