I installed a new Harbor Breeze fan and had a slight gap because of the original box placement. Also, the screws were exposed. This part addresses both issues. The ring joins together with a small press-fit dovetail connector, which is a little tricky to press together with your arms overhead, but it works. Maybe someone will improve the connecting mechanism.

If you need to adjust the size, you can scale in your slicer software or use the included Blender file.