Using two standard sized (19mm, ¾'') PVC pipes of 32cm long you can store 8 spools of filament inside one cubicle booth of an Ikea Kallax closet.
The standard European (light yellow coloured) electrical conduits have the same dimensions (19 mm or ¾'').
No need to screw anything since the pipes hold the stands straight.
The author marked this model as their own original creation.