Ender 3 filament holder an' stuff

filament holder with print-in-place swiveling filament sensor mount.

uses the original spool holder and:

4 m5 screws

2 m5 nuts

2 m5 T-nuts

1 m3 heatset insert (or you can use the on_dees version that uses an m3 nut)

3 m3 screws

2 m3 nuts