This is an easily mountable and movable filament spool holder, designed for Joel "3D Nerd" contest. It is designed to be moved anywhere along a wall of shelves and can slip between the outer rims of spools already on the shelf. It holds well on the rail of the outer shelf rail but increases stability by the long triangular section that rests against the bottom of the inner rail.
The goal was a filament spool holder that was easy to print, no supports and 20% infill (you may get away with less). It easily supports the weight of full spools. It was also made to be simple to use and move and adaptable to a wide variety of spools.
This can hold a variety of spools with different diameter holes and up to 75mm wide. The retainer lip keeps rolls from falling off. The roll rotates easy but not too easy, as to easily unravel from momentum.
My version 1 was designed as a 2 piece snap together so it could be printed an small build plates.. I did not submit that one. This version 2 (1 piece) submitted is much stronger and just plain easy to print and use. I just got it onto a 200x212 plate going diagonal. Many printers have bigger build areas. For small plates, the 1 piece can be divided in CAD or some slicer software then printed as 2 and then glued.
This was able to be printed diagonally on an old Reprap home build and printed much easier on a modern CR-10.