This is a simple 40mm fan mount I designed for the Hobbyking Print Rite 3D printer. There are a lot of different designs out there, but this is my take on it. To mount, I just used double sided tape to stick it to the front of the extruder carriage, so for it works well!. To power the cooling fan I ran a 12 volt supply from a fan port in the front control PCB to the fan.