My whole collection is here: https://www.thingiverse.com/Matsemann/collections/matsemanns-ambiguous-cylinders https://www.thingiverse.com/Matsemann/collections/

My whole collection is here: https://www.thingiverse.com/Matsemann/collections/matsemanns-ambiguous-cylinders https://www.thingiverse.com/Matsemann/collections/matsemanns... Do it, I have shown these to various school classes. They have been popular everywhere, from primary school to universities!