It is a mod of the Ultimaker 2 that transfers its extruder on the very top of the feeder:
It's supposed to attempt reducing the underextrusion issues (see http://umforum.ultimaker.com/index.php?/topic/3261-ultimaker-2-extrusion-problem/page-2
you've two parts to print:
- The block.stl, this part binds the extruder on the very top of the feeder.
- The tube.stl, this component is a guide tube which goes in the feeder, as the guide tube will now enter in the filament pusher carton on the top, and not on the back