Filament sub spools for sample packs

As I recently got 15 filament samples as a present, I quicklyrealized how hard it is to store them efficiently. On regular spools, they would take far too much space, to wind/unwind is annoying, and to print without spool will cause problems.

The following design solves this issue. In short, it consists of a replacement central cylinder for common filament brands ("filament-pm" and "prusament" spools), and a set of independent sub-spools that can easily be added or removed to the main spool.