what is this

The little plastic nut thing that is the nut for a screw holding in the Front turn signal. Having trouble searching for one because no idea what to type in lol

I’ve been trying to tighten my serpentine belt after replacing my alternator and whenever I attempt to tighten my belt this piece of metal ends up rubbing against it. I’d doesn’t appear in any of the video tutorials I’ve seen and I didn’t take a picture ahead of time so I’m not positive if it...