EDIT 2: After some extensively print sessions, I found that MK7 needs a NEMA17 with 2A coils. The 1A one spkip steps due to high torsion. For those who doesn't have a 2A Stepper, that's the MK8 version: http://www.thingiverse.com/thing:399731 EDIT: it works!!! printed and mounted! New Photos added! This is a preliminary version of my Bowden MK7 Extruder, suitable for Rostok, Prusa i3, etc. I derived this from another Bowden extruder for MK8 pulley. I completely remade it from scratch, is parametric but not compatible with the 3mm filament, due to 4OD 2ID push fit I use. Not printed yet (I'm printing it in this very moment, but no images ready yet) so I don't know if it is functional. If someone want to test it, print the idler and the extruder with 95-100% infill for durability. It's been designed with Inventor LT 2013 and quite tested for tolerances and resistance. Possibly I'll modify the idler to make it more strong against torsion due to hard filament pressure against the ball bearing.BOM: 1x BallBearing 626ZZ 1x 3mm nut 3x 3x15mm bolt (steel) 1x 3x40mm bolt (steel) 1x 4x3mm hexagonal bolt 1x 3x5.5mm bolt (idler) 1x 4ID x 20mm spring (I used one of the Wade Extruder Idler) 16x 4x10mm washers (spacers between the Nema 17 and the extruder) 1x MK7 Pulley EDIT: Something missing... -.- 1x PushFit 4mm x 5mm screw