It is some sort of guide for flexible filament. I have seen this kind of modifications on plastic extruders.
So I designed it from scratch for the all metal extruder of my Geeetech I3a, it fits with no modification.
24/05/15 Major update :)
Two versions now.
The 4mm is intended to be used with tubing - see picture (It's polyurethan, I have ordered teflon) Didn't test it yet, but...
Tested the 2mm version with filaflex, it works perfectly!