These are the bases for the marker lights that go on the tailgate and dually fenders on dually pickups. They screw onto the body panel, and the light lens clips into it.
The factory used 2 amber lenses on the front of the dually fenders, and 2 red lenses on the rear. There was also 5 lenses on the bottom of the dually tailgates. All mount with these brackets.
Brackets sold individually.