To clear extruder jams, I sometimes have to remove the cooling fan when it's running.
But...I'm clumsy and sometimes I stick my hex wrench into the fan blades instead of the screw socket hole, damaging the fan blades. Sometimes they break off entirely.
To prevent my ever doing that again, I added this fan guard with slips over the fan and stays on with a friction fit. It has gaps large enough to let air in but small enough that I can't accidentally stick my hex wrench where it doesn't belong. And it doesn't cover the fan's screw holes so I can remove the fan without removing the cover.