Printrbot Simple Metal Feeder Tentacle

See it in action here: https://goo.gl/gv60W8

This is a neat little doodad for attaching to the filament feeder of a 3D printer. As the filament is fed to the extruder it will spin. You can tell at a glance that your filament is extruding or retracting properly. There are 2 versions: a tight gap and big gap. The tight gap is just big enough to fit snugly. It SHOULD stay on with merely friction. However if you don't want to risk it falling off, get the big gap tentacle. There's a little extra space in it for a single drop of hot glue to make sure that it will not fall off and into your print.

This should fit any printer that has a similar feeder mechanism. The hole is 5mm at it's widest point for the tight tentacle.