This is almost the original NEMA 14 extruder for FoldaRap but with options for different drive gear sizes or bowden attach systems.Open the SCAD file and modify the hobbed and the bowden adapter diameter. The example STL is compatible with something like MK8 drive gear and RepRapPro bowden start. In this case, you need a 623 ball bearing instead 603 plus an M3x(whatever between 10 and 16)mm screw.