This bracket mount is designed to slide onto the long edge of a Cobblebot Basic/Beast carriage, and has two pockets angled just downward enough to ventilate the part extrusion zone with a pair of 5015 style blower fans (aka centrifugal or squirrel fan, 50mm diameter, 15mm deep). The fan angle also permits them to pass under the gantry rail when moving to Y maximum position.

For this build, I used the following fan:
http://www.amazon.com/Brushless-Cooling-Computer-3D-Printer/dp/B00THZK270