My original fan guard was V6 over a honeycomb mesh. The problem is that Noctua fans are so quiet that you can't hear them running. It was too hard to see through the mesh to check to see if the fan blades were actually turning. This is just the V6 logo (Shout out to Toys cuz I took the V6 from a Print screen of a video he made) in a circle. I can now glance at the fan and see if it is spinning. Because the 40mm Noctua fan uses M5 screw holes, I also included a file for some pins. Since my fan sits at an angle, gravity keeps them in place. If yours is vertical, just print then a little bigger and they will be held in with friction.
Extruder temp 225C
Bed Temp 70C