Ceiling-mounted spool holder

The usual bracket-mounted spool holder of the Prusa i3 optimizes footprint. Since I set my machine up in a closet I tried to minimize vertical space without wasting any shelf surface by placing the spool right next to the printer. So I created this spool holder which attaches to the shelf board above through four short wood screws.
Additionally four m3 screws and nuts are required to attach the outer frames to the top frame.
The spool itself rests on a cylindrical rod, which can easily be removed together with the spool through a cutout on the back, making it easy to change spools.