CR-10 40mm stock hot end fan mod

thingiverse

Hopefully this is accurate as I made it from aluminum in my workshop and then came back to my PC and drew it out from memory. The concept is that it will obstruct some airflow coming from the bottom of the fan, thus not cooling the heater block, and you might even be able to run without a blanket on your hot end. If you're 3D printing it with ABS recommended, although with a fan blowing directly on the part nearest the hotend, you may get away with PLA.