This is exactly the same as http://www.thingiverse.com/thing:961630 except it is designed to feed filament into a Bowden pushfit connector.
The diameter of the Bowden pushfit connector is configurable in the source, by default it is 9.5mm. Filament diameter is fixed at 1.75mm, since using 3mm filament with a Bowden system is not recommended.
The extruder body can be rendered with or without a mounting bracket. Example code for a basic mounting bracket which can be screwed to a 2020 aluminum profile is included.

Everything else is exactly the same so please refer to the original 30mm version for details, attribution, comments, instructions, etc.

Again, complete OpenSCAD sources are available, including those for the fishbone gears.

Please be sure to read the source code and render the parts according to your setup before printing.