Prusa MK4 spool holder remixed to fit Ender 3's and other printers with 20x20 aluminium extrusion.
There are two versions, the one with four screws is recommended if printing a single holder, but for a dual holder you can use either one.
The four screw version hasn't yet been tested, but it should work fine as it's only a small change.
Please report back how it works for you!

The author remixed this model.
Modified to fit printers with 20x20 aluminium extrusion.