Low Profile Spool Holder

Low profile spool holder for 2020 Misumi extrusion, similar in design to the [Kossel compact Filament Spool Holder](http://www.thingiverse.com/thing:312624) which inspired this version (Thanks Elliot for the suggestion). The spool fits over the small hub, and the hook drops in from the top to hold the spool in place. The hub is small enough for Taulman's mini spools, and short enough to fit in the stepped spools from Ultimachine and Atomic Filament.

Requires a 10mm OD, 5mm ID, 4mm wide be