Helix Design 30mm Fan Guard
WTF fans spin at an extremely high rpm. If you accidentally stick your finger, a tool, or some other object in the fan while spinning the outcome is not going to be beneficial to either you or the fan.
Two mounting options available. Integrated to the design is a corner clip so only one screw is required to hold the cover in place. This option is nice for some fan mounts. Or you can use two corner screw mounting locations.