My daughter struggles with all the loose ink pen cartridges in her bag, so I designed a compact storing solution for them.
Use an M3 screw (12mm max length) and two m3 serrated lock washers to screw the 3 parts together. Align the cap with the drum before tighten everything together.
If the barrel is not turning smooth enough use a file to carefully file down the notch a bit. Then tighten the screw to fit the snapping haptics to your liking.
The author marked this model as their own original creation.