Summary

What you need:

• 4x shim washer 1mm width
• metal axle (8mm when using the spool spirals)
• 6cm teflon pipe (when using the duct)

For the box, i used the Lock & Lock HPL714F Multifunktionsbox Slender 4,3l, this fits most of my filament spools.

Thanks to the inventors of the duct and the spool holder spiral.

Update:
Long end cap added.