NEMA 17 (42mm x 47mm) stepper motor cooler. Suits 40mm x 40mm x 10mm fan.

thingiverse

Both left and right exhaust to avoid blowing onto printer bed. Would advise printing in abs with at least 70% infill to avoid warping. Fans are a tight fit to avoid having to use screws. If the fan clicks while running, it's too tight. Just sand the side a little.... update 1 Added version with cable tidy and zip-tie holes. update 2 Added a "twin fan" version to help cool head.I found once inclosed, while printing ABS the head/hot end inlet gets too hot. This caused the ABS layers to remain too soft and jams due to material getting hot too quickly in the nozzle.