My special designed filament holder are directly for the original ULTIMAKER 3 (UM3) spools.
Until now I use it for the 350g and 750g spools of 2.85mm filament (see pictures).
Easy to clamp or unloose in the spool
Best way of storing the filament spools
Spools are better stackable
No unraveling of the filament
End of filament doesn't have to be fixed in the small hole and the danger of breaking filament
I'm looking forward to your feedback and especially if it works as well for the other material spools.
Posted at https://www.thingiverse.com/thing:2746539