Parametric Auto-Rewind Spool Holder

Newer design available: [Universal Auto-Rewind Spool Holder](https://www.thingiverse.com/thing:3338467)!

Filament load/unload issues? MMU2 taking too much space? Not with this Parametric Auto-Rewind spool holder! It keeps filament on the spool during unloading, up to eight full revolutions.

This is a remake of the original [Auto-Rewind Spool Holder](https://www.thingiverse.com/thing:3200204), but with significant enhancements:
- Fully parametric
- Default spring size 100mm gives up to eight rewinding revolutions
- Metal bearings can be used, but also works fine without any bearings
- No tape or zip-ties needed
- Compatible with existing spool stands with 8mm axle slots
- Spring blades in the hub keep the spool pressed against the backplate for adequate friction and prevention of spool sliding off the hub
- Adapter allows to mount differently-sized spools on the same hub
- Spacers included to keep hub in place
- Spring guard included

How it works:
- Enter your spool's