Summary

This fan guard is designed for 60 mm fans but can be easily resized for other fans. The part is designed to fit a 64 mm or 2.5 inch hole and will snap into a 3 mm thick panel due to the small nubs around the rim.

I used this fan guard on my HyperCube printer to allow me to place a Plexiglas panel over my electronics bay but still allow the power supply fan's air to exit the enclosed area.
https://www.thingiverse.com/make:406713

The fan guard should be printed facing down as presented in the STL file.