This is a shim, your car is likely full of them on the front sheetmetal bolts.
This one is actually for wheel alignment purposes because it has the little "handle" on it. Fender shims don't have that handle but for some reason I couldn't find a photo of one. Personally, I see no difference in using the washer other than it is round instead of square. And, for that matter I have gotten washers and cut them with tin snips to make what ever shape you want. Take a large fender washer and then cut off two sides and you have a shim perfect for the lid.