fan duct 40mm

This is a fan duct that you can put on a 40mm fan on a 3d printer for example. The idea is to reduce wind noise by making a aerodynamic profile to make the air flow better. It changes a bit when you have a powerful fan but on a 3d printer the effects aren't really impressive.
But it's nice and looks cool. Resemble a plane turbine.
It's made to fit m3 bolts.