Small clip that attaches to the edge of the spool. Holds the end of the filament in place so it doesn't unraveling when in storage.
Updated version can be found here:
-- Octave Natural ABS
Use the "Up Spool Clip" for the OEM Afinia / Up! filament and the "Octave Spool Clip" for filament that comes from octave.com. You will probably need to adjust the orientation before printing.