I decided to play around a bit with making fans. These are designed to print without needing support material, and the first version came out great on my Ender 5 plus... It also exploded when I was playing around with it because I accidentally smacked it with my hand, so no photo unfortunately. :/ Let that be a lesson though, hard plastic spinning at high RPM can be dangerous and may result in energetic catastrophic failures. Use proper precautions.
The hole on the fan is made for the 775 motors I have. They've got a 5mm shaft with a 1mm key slot.. The fan is ~200mm wide so it might be a tight fit on some printers. Seemed to move air alright, wasn't able to verify at full power because my test bench power supply maxes out at 5amp draw and the aforementioned explosive hand incident.