Fan duct

When importing the stl. Split to parts and change some settings on the part that should become the grill

• Set the bottom and top layers to 0, for the grill piece (after you split to parts)
• Set the infill to a pattern you'd like, with the infill ratio that you want. The higher the infill ratio, the smaller the holes. By default I use 30% Grid. (As an example: 3D honeycomb gives a nice “3d” maze for the airflow, or you can just use a 15% rectilinear for a rough grill)
• The alternate extra wall setting creates a nice strong grill, if your slicer supports that.

It's designed to be printed as one piece, but you can also print it in two pieces and glue 'm together.

(The model is parameterised, so I can generate other sizes as well if you want, just let me know.)