I have updated the .stl files so that the parts are paced and oriented better. I am using Cura for printing so I initially did not realize this could be an issue. Extruder that I made for my Cyborg 3D printer. Uses 12mm shaft and gives very good grip. Pulling force is about 60 Newtons. You will need two 6001 bearings and one 608 bearing. Ready to be connected to E3D 3mm bowden version hotend. I have made a strength test and the extruder is able to lift 5,5Kg weight (12lbs) hanged on the fillament. That is about 55N of pull force on the fillament. No slippage, no step skipping with 0,5N/m NEMA17 stepper motor. http://youtu.be/M3KoYmaYrjM