The screws that secure the decrative cover over the ball bracket and wireing are not long enough with the ceiling medallions installed. These are specialty screws that secure a bowel like cover and then have a gap for a washer like painted ring to slide on, to cover the screw heads securing the bowel like cover. Not sure on the name brand it was purchase 4 yrs ago from either Home Depot or Lowe's.

HD and Lowe's have a whole aisle of screws and ornamental washers with threads like 8/24, 8/32 and 10/32 which are common to electrical boxes. Even inported fans use SAE thread screws although the bolts may be metric.