In our house there is still an old shelving system (which is actually still being sold) made of metal rails that are screwed to the wall and metal brackets (e.g. 20cm) that can be hooked in at different positions. This allows very flexible shelving systems to be built. With the 3D model designed here, the metal brackets can be converted into a holder for two rods, which are very well suited for storing filament spools. It is a fast print. I still had rods with diameters of 16 mm and 20 mm; a model is included for both variants. Simply print it upright on the closed edge with the slot facing upwards.