I have designed this adapter to be able to fit eSun 2.5 Kg spool onto standard MK3S spool holder. It barely does, but seems to work for me. Also, it is nice to have counterweight spool on the other side of the holder to help it be more balanced.
To set it up, you will need to remove the side of the spool holder you plan installing the adapter to. Then feed the adapter onto it and reinstall. There is a cutout in the adapter to allow use of a screwdriver to gain leverage in order to screw the whole assembly back onto spool holder. Now, just add the spool and secure it with the retainer clip.
The author marked this model as their own original creation.