95 mm Fan Guard

Print it with somewhere around 10 % infill, 2 mm perimeters and no top and bottom layers.
To mount it just slide it over the fan.

Update 2018-10-21_14:18
The first version works fine when the fan is blowing downwards. But when operated sideways or blowing upwards the fan could/will come in contact with the fan-guard, since there is a little play, producing an annoying sound and slowing the fan down.
I made a minor change to the design to add an additional clearance of 3 mm. As a nice side effect the guard is now more rigid, thus the claws are now holding much better than before.