Okay this might not support 3kg spools. Not even 1kg spools but it is perfect if you still don’t have a spool holder but want to print one. Some left over copper wires and a office clamp are enough for 10-12 meters of filament.
While putting together my Two Up 3D printer I did not want to glue the x-axis belt to the extruder head so it could be removed easily later on. I used two small zip ties to connect the extruder head to the belt.