as at 20 22 disposed at the the distal end of each leg 18 of the core 12 as in evident each retaining member possesses a flange like exterior periphery slightly larger than a single face of a smaller cube 14 thereby to overlie in part all cubes along its face of the primary cube it will be evident that with the slight overlap shown it is not possible for any individual cube 14 to drop or fall from the assembled relation of the main cube 10 nonetheless each of the smaller cubes 14 is free to slide laterally or vertically into the single hole or void cube space provided in the cubical array in one form of the invention the retaining members 22 are formed as integral one piece elements with the associated leg 18 thus for simplicity the central core portion as seen in fig3 may be readily molded from plastic in essentially tubular form and wherein the four legs 18 lying in one horizontal plane will each have formed thereon a laterally outwardly directed flange thereby providing the retaining member as at 22 for simplicity the vertically extending legs 18 have no such flanges thereon but rather are provided with.