groove mount 1/8" NPTF pushfit adapter (1.75mm/2mm ID, 4mm OD)

Extruder groove mount to bowden pushfit adapter. Like [E3D's version](https://e3d-online.com/bowden-adaptor-1-75mm-filament), just for [1/8" NPTF Pushfit Adapters](https://www.mcmaster.com/#51025K171).

Using the fantastic [OpenSCAD Threads library](http://dkprojects.net/openscad-threads/).