About this 3D model

This is a hot-end bowden coupling. The PTFE tube will guide the plastic. On the ends of the PTFE tube you can have a M6 nut that will be held captive by this coupling but it can be removed sideways. More information on the bowden extruder can be found here: http://reprap.org/wiki/Erik%27s_Bowden_Extruder Rustyspoon also made a version (thing:2825), but it uses more plastic than needed and the STL is not oriented for correct printing. Otherwise, that one is a robust one that you just need to rotate before printing.