Filament clip (3mm and 1,75)

There are many others, but I wanted a minimal and nice design that does not protrude outside of the reel (so you can stack them without launching an edge clip).

Use the two last loops of the filament. Insert the first loop in the clip, pull the end of the filament tight and then insert the second loop in the clip. It works because the two loops want to go straight and work against each other.

The pictures are of 3mm filament. I haven't tested the 1,75mm one, but another maker did (see