Abstract: A plurality of extruded aluminum structural modules of selected different peripheral sizes are configured to be disposed in adjacent coacting positions so that a selected number of such modules assembled together form a peripherally enclosed modular structural member. Each module includes components of module positioning elements in the form of splines sizes and configured to coact with mating module positioning elements of the other structural modules to facilitate assembly of modules into a structural member. Force applying devices, such as HELICOILS are disposed to urge the module positioning elements together to insure the integrity of the assembled modular structural member.