More details on the Bowden extruder system: http://reprap.org/wiki/Erik%27s_Bowden_Extruder

I just made a serendipitous discovery:
I printed a very narrowly fitting freely rotating coupling and it had such a good grip on the PTFE that I printed another with just a little more contact area. You don't need the nut anymore for the Bowden cable!
I had been looking for push to fit couplings ever since Charles Pax showed me how good they fit to 1/8" PTFE cables. Now it appears that they are definitely printable!

The current push to fit coupling can be removed sideways. If you pull it sideways at the top first, you can pull it out with the plastic filament inside. It's a huge benefit to not have to pull back the plastic first.

A variant with a clip that you can pinch with your fingers would perhaps be even better, but this one is so simple and very functional and it hardly takes up any space.

I also included a cable to cable coupling, you just put in two cables sideways.

When done correctly, this type of friction from printed parts could be used for the extruder drive mechanism too, replacing the metal pinch-wheels that we currently use. In any case it can already withstand more than the force the force that the filament is driven with, and that's with ultra-slippery PTFE!

It would also allow us to print fasteners! Though perhaps a simple plug and a cam mechanism will better do the trick. And if you get a similar friction fit on the filament itself, you can start ysing that as structural material too (with some creep, but you could re-tension things once in a while).

Which other non-printed parts can we eliminate by a superior (I'd like to think this is an improved part, but only time will tell) printed alternative?