A mini filament spool, pictured with the sample filament from my Ender 3 V2.

Remixed from:

https://www.thingiverse.com/thing:427024

The walls are a bit thicker, the width between the ends a bit wider, and the diameter sized to fit on the spool holder I use for my M3D spools:

https://www.thingiverse.com/thing:4640027