Nylon nuts (also called screw grommets) are designed to attach side marker lights and various trim panels. They usually fit into a square hole and accept various screw sizes. This design allows the applicator to fasten the marker light (or panel) securely without the nut spinning in the hole. It also acts as a gasket for water leakage.
Looking for a part #. Then sort by Ascending, and click Filter - to alphabetize part #'s.