This part clips onto you MakerBot filament spool [1] to keep the filament in place during transport or printing. It is designed to work with the MakerBot filament spool holder [2]. The housing freely rotates around the spool as filament is removed.

[1] http://store.makerbot.com/plastic.html
[2] http://www.thingiverse.com/thing:7105

1) Print out 5 or 6.
2) Clip them onto you spool.
3) Clip the spool onto your spool holder.
4) Rock!