Bottom side of barrel for spool holder

This is an add-on for [Hogsqueal's awesome hanger setup](http://www.thingiverse.com/thing:804897). I ran into an issue that when the filament runs low, the spool tilts up and mostly off of the hanger.

If you slip this thing over the part where the spool rests, you can effectively get a full flange on the end of the peg, keeping the spool in place through its lifetime. I actually ended up preferring this "band-aid" fix to a redesign of the hanger because it doesn't make it any harder to get th