This is my wall mounted Spool holder. It fits 1 used and 6 inactive spools of filament through the help of a 15cm long 8mm thick threaded rod. The are mounted the following: nut, washer, wood, washer, nut. To hold the used spool i use two ordinary wooden corners, which are simlpy screwed onto the board. The board dimensions are 40cm x 100cm. On top of the i glued the two rodmounts. The spool hangs on a 7mm Ø alubrass rod, The rod is glued into to grip with two component epoxy glue. The exactly measurements you can find in the attached schematic.