Summary

Found a plethora of spool adapters but none that fits my needs exactly.
So as I love OpenSCAD i fired it up and created my own design which is very similar to other threated spool adapter designs.

You can print with no supports and i would recommend either 0.12mm layer height for the threats or a profile which uses adaptive layers feature and would greatly reduce print time, as most of this model can be printed in 0.2mm layer height.

Embedded the threads Library from Dan Kirshner

[Update 1 (2020-05-31)]
as it's difficult to predict how it will fit to you actual spool I made a Simulation-View.
Enter dimensions of your real spool and it will display the assembly with spool.

Parameters explained

Unfortunatly the customizer app doesn't work as expected. You will have to download the .scad and use the customizer in openSCAD.

Dimensions of resulting object are calculated for worst case. So the length of the treated part will always allow to that each paring of diameter and width will allow the nut to be screwed at least completly to the screw.

This means a spool with the maximum width and the minimum inner diameter will have the nut at the far end of the screw and the other way round the nut will be screwed as much as possible having the screw part protruting.

If you want to have the screw part smaller you can set the minimum spool width bigger than the maxiumim spool width.