This is the simplest possible extruder blower for the Geeetech i3 ProB.
It is meant to house e standard 40 mm fan in the simplest possible arrangement.

If you have the Geeetech i3 ProB then you already know how much it needs a blower .... this is the simplest way you can make one for yourself without needing one to complete the print.
The little vertical hole is meant to house a piano wire to help guide the cables aid their ware on the X axis. Just wrap it with the cables for some 20 cm and put the loose end in the little hole: your extruder assembly cables will be grateful. I also like to put some sort of sheath on the piano wire so it can slide fleetly in it while the sheath stays stationary in the cable wrap.