Customized version of http://www.thingiverse.com/thing:188358
Created with Customizer! http://www.thingiverse.com/apps/customizer/run?thing_id=188358

Using the following options:
Vane_Width = 1.6
Bolt_Diameter = 4.5
Grille_Height = 2
Vanes = 3
Rings = 1
Standard_Size = 60
Ring_Width = 1.6
Bolt_Hole_Width = 71.5
Edge_Width = 3
Hollow = no
Grille_Width = 80