Fan duct for Prusa i3 rework extruder

This is an alternate fan duct for the 40mm fan attachment to the Prusa i3 Rework style extruder. This is also the fan duct included in the reprap Wilson design, and I'm copying it here in case any Rework users want to give it a try.
I designed this in Sketchup to improve airflow at the extrusion point, with some air also directed at the top of the hot end to prevent heat creep. With the original fan duct from eMotionTech, I found that I had to choose between directing airflow at either the tip or the barrel of the hot end, when what I wanted was a little airflow to each (but not at the nozzle itself).
Note! You may not want this fan duct if you are printing ABS, as airflow on the model is not very helpful for that material. But for PLA, I am very happy with the results.