Bowden cable coupler

This is a Bowden cable coupler. It joins Bowden cables. Filament passes easily from one cable to another. With an M4 nut, the grip on a standard sized (4mm OD) bowden cable is strong enough not to detach during prints. One side lets you slip a Bowden cable in and out to allow for easy detachment.

##Why?
* Easy to detach
* Corrects mistakes made from undersizing Bowden cables
* Allows coupling tubes of different material, e.g. teflon with PEEK.

I started making this design after finding it difficult to remove the Bowden cable from the [Hotend](http://www.thingiverse.com/thing:378928) I'd designed. I'd tried store-bought couplers for threaded rod, but realized most stores do not stock couplers small enough to grip the cable. A store bought 10-24 coupler would simply slip off the cable during prints. I realized I could use M4 nuts if I printed out my own interface.



I'm thinking to use this eventually for printing polycarbonate with my hotend - just hook up