I believe that there is a threaded insert. I have always had problems with the screws working out and have reverted to using Loktite there and on so many other points of this car. It is, after all, literally trying to shake itself apart!
A rivnut - maybe just buy a kit of them from Amazon et al?. Just changed my socket screw to a bulb head M6x25 to hold a badge bar, and added a locking washer.
