A very simple spool holder made for printers on shelves, under hutches, etc. This can hold two spools, although it would be a tight fit (or you can just print it bigger). It can be fastened to a shelf one of two ways: (a) using the hole in the top, screw it into the shelf (wood shelf) or zip-tie it to the shelf (wire shelf), or (b) using the notches on the sides and hook on the top, tie it to the shelf, looping around the back (this is the method I used).
This is meant to be printed without support, although a raft is recommended. I printed it at 0.3 mm resolution.
Once it is printed, attach the ends to your shelf and simply snap the rod into place while the spool is on it. The flat side helps with both printing and snapping the rod into place.