I didn't like the fang designs found on here, since not all of them would fit my higher Noctua A4x20 fans, that are 20mm high. Others were not optimized in airflow. So I took some inspiration from a few different models, and modelled a version myself in Solidworks.
The part fits tight on the stock extruder.
Main inspiration sources:
I have found that the current setup might result in loosening the hot end screws, they need to be mounted really tight, or use loctite blue.
By making the holes on the cooling duct bigger, the original screws are mounted directly on the hotend cooler. The whole print cooling fang will sort of rest on the 2 screws, it isn't necessary for this to be mounted super tight like the hot end. I haven't been able to actually test this.
Edit 21-3-2018: Uploaded the the original Solidworks drawing as requested.
Edit 5-12-2018: Uploaded different versions with different mounting holes for the hotend screws.
Also uploaded a new fang with the option to mount two 40 mm part cooling fans.
Used Simplify3D to print. M3 tap on the 8 holes to mount the 2 fans.