Abstract: A hollow block (e.g. a rectangular prism) preferably has six (6) perpendicular faces. Each face preferably has a wall with a particular thickness. An opening is provided in at least a particular one of the faces, and preferably in all six (6) faces. A hollow beam (e.g. a rectangular prism) preferably has six (6) perpendicular faces. Each face is preferably defined by a wall with a particular thickness. An opening is provided in at least a particular one of the faces, and preferably in the four (4) faces defining a closed loop, in the beam. Substantially parallel snaps extend from the other two (2) beam walls and have at their outer ends portions shaped to facilitate insertion of such snaps into the opening in the particular face of the block, retention of the snaps by the inner surface of the face defining the opening and removal of the snaps from the opening. Such portions are shaped for the beams to be pulled, peeled or bent from the block.