This fan mount is used in the place of the laser cut extruder tensioner piece that probably comes standard on the current versions of the Simple (Mine is an upgraded beta test model). The mount simple snaps into the original laser cut piece and can be held in place with a small zip tie. 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.