[Update after a few months of usage] Some refill coils may push the spool walls outwards and you may end up with a ruined spool. To prevent this, apply a bit of superglue to the grooves or ridges of the adapter

— Initial description —

The initial model lacked holes for securing the filament end and relied on the spool walls to keep it in place. This remix features two holes at the bottom of the adapter for securing the filament. I've also added a small lip on the other side of the adapter, ensuring a better hold on the filament until you push in the second spool wall. If the description doesn't make sense, you'll understand once you take a look at the model ;)

Push the end of the refill filament through the two holes at the bottom and place the coil onto the adapter. Then push the side with the two holes that hold the end of the filament into the first spool wall. Cut the zip ties, ensuring that the coil stays below the lip. Finally, push the second spool wall into the adapter.

Slice it with 1 wall and 4% cubic infill and you will use less than 25 grams of filament for 1 adapter.

Check the description of the initial model for more details: https://www.printables.com/model/431304-simple-prusament-to-masterspool-adapter