Within the union systems for shelves are the moon couplings, these have the Luna coupling bolt, 9. This piece has a diameter of 6 mm at the end of the same and a length of 9 mm in the body of the bolt, it has spiral notches to ensure screwing. The star head of this bolt has a diameter of 10mm and is 8mm long. The packaging of these pieces contains 2,500 units and they have been made of resistant steel with a zinc-plated finish to protect it from corrosion and oxidation.