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:

Ring_Width = 2
Vanes = 6
Hollow = yes
Grille_Width = 40
Rings = 4
Grille_Height = 4
Bolt_Hole_Width = 71.5
Vane_Width = 2
Standard_Size = 80
Edge_Width = 2
Bolt_Diameter = 4.5