Flange bolts are machine threaded for use with a nut. They have a flange under the head that acts like a built in flat washer.
A hexagonal head for use with a wrench. (Note: Shorter lengths are found under full thread.) Meets DIN 6921 (1983). Flange bolts that are non-serrated are sometimes called frame bolts.
Flange bolts have a flange on the bottom of the head that distributes the load like a washer.