Abstract: An apparatus for joining sections to a knuckle in a spatial structure and including a first hollow base piece having a substantially spherical shaped out shell provided with a first plurality of equidistantly positioned holes and an inwardly bent perimeter area, a second hollow base piece having a substantially spherical shaped outer shell provided with a second plurality of equidistantly positioned holes, components for joining the first and second hollow base pieces to each other to form the knuckle with all holes of the first and second plurality of holes equidistantly positioned from each other, an internally threaded single piece element, a section having a face and being rigidly attached to the internally threaded single piece element so that the face rests upon the outer face of the knuckle, and a tightening screw having a head resting on the inner face of the knuckle and a body passing through one of the equidistantly positioned holes of the knuckle so as to engage by threading the single piece elemen