Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3934123.

This is a wall mount bracket designed to work with the Prusa T style spool holder posts. Or, if you don't have those, an easy to print post.

Most spool holder posts on Thingiverse are designed to print in the Z direction, which is the weakest direction, or with a lot of supports. By splitting the post in half you don't need support and will be applying force in the strongest direction of the print.

Installation is easy. Insert the post into the holder and twist clockwise (looking from the back). Install the bracket so the split in the post halves is vertical.