I made this combo fan mount and duct to direct the air to the nozzle tip to cool the filament quickly. This little guy greater increased the quality and speed of my prints.
The mount slips under the extruder motor and there's a window in the mount so you can thread the fan cables through. The holes are spaced for a 40mm (outside case dimensions) fan with holes at approx. 33mm apart.
Printed on my Printrbot Simple V2 at 45mm/sec, 0.2mm layer height and 10% infill.
I bought the fan on Amazon:
Scythe 40x40x10mm Fan 2 pin with 3 pin adapter.