This is a fourteen-sided die with cuboctohedral symmetry. The hexagonal and square faces are exactly the same area, so they are equally likely landing positions. I've verified that it's fair to within 0.5% with 600 rolls of this die. There's a 0.1mm hole in one of the square faces to ensure that software sees it as hollow. The hole is too small to be visible in the printed version. Also available on Shapeways.