Ceiling box cover by Arlington used to cover unused 3-1/2 in. and 4 in. round and octagonal boxes prior to the installation of a fan or fixture. It has a deep, attractive cover with no screws showing on the outside.
The threaded post pushes in for flat ceilings.
Non-rusting, paintable PVC.
Plastic eliminates the scratches you get with painted metal covers.
Covers poorly cut drywall.