There is some confusion, at least on my part, about this fastener. The master parts catalog calls for the grille to be held on by a combination of 56904's and 610019's. But, Rusty has all 610019's in his grille, so maybe I put the wrong screws in? Anyway, the 56904 looks like the screw in the first picture. In fact, I think it is as the Standard and Utility Parts Catalog says it is - a self-tapping washer-head #8-18 screw that is 3/4" long. And, that's a perfect description of the screw in the picture, which is a 56912.
But, as said, I have the 610019's in Rusty's grille, and they look like the top screw in this picture: