Flange bolts have a circular flange under the head that acts like a washer to distribute the load. Flange bolts that are non-serrated are sometimes called frame bolts.
A hexagonal head for use with a wrench. Meets IFI-111 (2002). Serrated heads are designed to resist loosening.
Flange bolts have a flange on the bottom of the head that distributes the load like a washer.