Sphericon (square base)

thingiverse

Print sphericon_smoother.stl twice. No supports, face down on a flat surface. Check out sphericon_square_assembled_dont_print.stl for the finished product. That thing has an unusual rolling motion. If you have small elephant feet on the plugs, that's perfect. Insert the plugs foot first into one side. They will click into place. You might not even need glue; it seems to hold together just fine as is.