I recommend printing these brackets with a large layer height for speed. 0.3mm layer height for a 0.4mm nozzle or 0.4mm layer height for a 0.6mm nozzle. Print flat side down on the bed. No supports needed. Use a brim for bed adhesion. Mine took about 5 hours each to print.
You'll need two, 1" diameter wooden dowels to mate with these brackets using #10 screws. If you're mounting on drywall, you may be able to use 48" dowels without needing to cut the dowels. I recommend checking your stud spacing first and then trimming down the wooden dowels as needed. Align the dowels to the printed parts, pre-drilling the dowel ends to the shaft size of the screw, to prevent splitting the dowels. Screw the dowels into place. Now you can screw it into the studs!
Notes:
I designed this to work with a 48" span, but you may get some bowing in the middle if you're storing full spools. You may be better off doing 32" spans.
The screw holes are designed for #10 screws commonly found at your local hardware store (in the USA — not sure what the metric equivalents are).
The author hasn't provided the model origin yet.