Reall odd "odd" ones. Not real sure, they don't look like they have a screw hole so could be used in lieu of a screw fitting, perhaps but then it wouldn't hold the motherboard in place. The screw part looks like a wider thread and one side is flat so it might be used like a "shelf" rivet (like in a book case to support a shelf), perhaps to hold a PSU in place?
It has a screw hole on top. I only received the sufficient amount of standoffs too.