After printing we all have to store our filament properly. One part is to ensure that the it does not unwind from the spoole.
I did this by threading the filament into the hole(s) on the edge of the spool what also means to loos 5 to 15 cm of filament each time I store it. And I did not like that and came up with this little tool. The part with the hole comes over the end of the thread, the other part could be clamped to the next thread / winding. By moving the tool everything tigthens up.

I'm pretty sure that I'm not the first on with this kind of solution but I'm new to every thing (fusion 360, slic3r, 3d printing etc.) I like to practice ;-)

As usual I've included a factory file with settings for my Prusa MKS2 and rigid ink PLA filament.

Update 2020/04/26: Got some complains about the fit so I've slightly enlarged the diameters

Print instructions

Category: 3D Printer Accessories Print Settings

Printer Brand: Prusa

Printer: Prusa Mk2

Rafts: No

Supports: No

Resolution: 0.1

Infill: 30 (but does not matter that much)

Notes:

I've added a brim to enlarge the surface on the print bed.