40mm Box Fan Housing v2

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