Quadstruder K7 - Dual Drive Extruder

*update: The brass gears are showing signs of wear after only a few months heavy use (see pictures). I would recommend using the [newer version](https://www.thingiverse.com/thing:2890048) of this design using stainless steel gears. If you use this version, get extra brass gears as they will probably need to be replaced occasionally. Since all the wear happens on one edge of the gear, you can also swap the two brass gears to double the lifespan before replacing them.*

Cheap 1.75mm dual drive