This surface is based on a 60-fold tesselation of three ribs of a skeletal icosahedron. With the symmetry of a dodecahedron, 12 pinwheel-shaped twisting holes divide the inside of the hollow sphere from the outside.
This shape was designed by calculating the vectors on paper, then rendered using OpenSCAD.
Diameter is 5.6 cm (2.2 in).
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