Mini spool I use to store my sample filaments.
Print 2 and glue together.

Print Settings:
3 walls
2 Top
2 Bottom
10% % infill
Layer height is 0.3mm

Inner diameter is 88mm
Outer diameter is 142mm

I can fit 4 halves on my 300x300 bed and it takes about 1,5 hours to print it. So it's about 45 minutes for 1 complete mini spool.
Not the strongest design but it works for me very well.

Use the small holes to fix the filament on to the mini spool.
Use the small clip to keep the filament's end in place on the spool when not in use.
The spool holder can be used on 40x20mm aluminium extrusions.
I've uploaded a 20x20 version but didn't test it yet

Enjoy !