N800335-S100

This is a stamped self-threading nut that is meant to 8mm plastic studs, such those on the marker lights and turn signals.  The S100 finish is said to be "special", so I don't know what color they originally were.  Anyway, they are 19mm (3/4") in diameter and are 7mm (~1/4") tall.  Or member Bryan/fryntrz found them from NAPA as Balkamp 665-1985, as shown in this post.