I used brass inserts at the hole locations. This ring was printed in ABS and mounted using fiberglass epoxy. Then bodyfilled/sanded/painted into a door window sail.
The grill is a 3" universal from amazon that slips into the ring lip.
Note: File is modeled in inches. Scale in your slicer for millimeters. Most slicers will automatically scale up.
The author marked this model as their own original creation.