Fan duct for 30x30x10mm fan for the kossel clear fan mount

This fan duct is valid for every 30x30x10 fan, but the lenghts are designed for the Kossel clear fan mount:
http://www.thingiverse.com/thing:372568

This duct is for cooling the extruder. Whithout it, the aire blown by the fan goes to the nozzle, cooling it too, in a way that it's impossible to reach more than 250ºC and slowing the heating.

The purpouse of the fan is avoiding the heat going up through the extruder body and preventing the jamming of the plastic or damaging the extruder its