They are called "nutserts" and it is common that they will spin when the truck gets older and a little corrosion happens between the screw and the nutsert. When they spin you have to hold the back of them, or drill/ grind off the screw head. Then replace them.
They suck however so a better way is to file the hole out square and put a RTC3744 plastic nutsert in and use a screw. That way, with no nutsert, the screw can never get stuck again during future services.
Side marker lights have them too and they are famous for sticking and/or spinning.
On the side mirrors they have a black plastic bushing on the screw that keeps them from backing off. Once you have the mirror off you can tap out the screws and you'll see the bushing.
I do not check PMs. Call or email if you need something.
ECR is not a parts source. We are not in the mail order business.