This is a small piece to allow you to mount the filament spool holder sideways. There are many adapters out there already, but I couldn't find one that easily fit past the Z rods (if you have dual Z rods) and didn't require unscrewing the top bar to fit it. So I made this.

No need for additional fixtures, you can use the existing screws + T nuts.

It was designed for my ender 3 but should work with any printer that uses 2020 extrusion.