A square is an example of a regular polygon. In general, a rectangle is not regular because not all of its edges are of the same length. Cube/ Hexahedron have six faces with eight vertexes. Industrial Products of various kinds are using cuboids (plate 6) which are visible in plenty.
Keep the equilateral triangle for the face, but now put four of them around each vertex. This yields the Octahedron, having eight faces and 6 vertexes with eight faces. Interesting product application found based on the principles of octahedrons (plate 7).
