UPDATE: I realized the screw holes to hold this together were incorrect (32mm vs the NEMA 17 standard of 31mm). No other changes.
Per a request from tigris, I revamped the design to allow two fans to be stacked. Also, the revamp allows all parts to be printed without support or a raft. There is now a middle section, one version with a slot for wires and one without. I noticed I goofed and the thick vane is actually on the wrong side for the fans to pull air in the right direction. If you just mirror the part in RepG or Makerware, that should fix that issue.
For a double fan arrangement, you will need M3 x 30mm socket head cap screws and 20mm for a single fan arrangement.