The Schuberth C3 helmet has two 15mm (about 19/32") holes for its ventilation system on the inside that have a direct connection to a large air intake on top.
That's a good idea, because your head gets cooled in summer, but not carried out the best way, because they forgot to add a fly screen between the shell and the cushioning and therefore now and then you get insects in between your head and the helmets shell, and sometimes they survive...
So I made this thing to prevent them from coming in. :)
I couldn't think of an easy way to provide this as an STL or such, sorry!
The GCode has been manually modified and optimized for 0,3mm layer height and 0,42mm string thickness.