I printed pit3k's bowden clamp and I experienced some difficulties to pass the filament through the riser. I made a subtle change on the riser hole which guides the filament through on the nut part. Now the nut has a conical hole and just 5 mm before the top it extends to fit the tightening ring into it.I also made a countersink on the bottom on the riser after the print by using a countersink tool (I tried to create this countersink directly in the model but it fails to print on a heated bed, even when raft was switched on).I also recommend to do another countersink on you bowden tube too.Finally, I printed chopmeister's great H3 feeder unit and tried to install this bowden clamp in it. It was OK, except that the riser was a bit loose so I made a small tightening nut too to fix this.Modified OpenSCAD source attached.To explain what I did I made a simple drawing - check the picture.I printed it with 0.1mm layer height, 100% infill.Update #20130329: the hole for the bowden tube on the top was too short and also the thread was not long enough if you wanted to use the tightening nut. I extended the thread by 5 extra millimeters and created a new STL (Feeder Clamp 5mm longer thread) and also increased the size of the bowden tube hole by a little in both Feeder Clamp STL files.