Flat Countersunk Nib Bolts are
threaded fasteners with a flat head and are tapered underneath the head. The Nib bolt has a nib which protrudes from the taper that will fit into a countersunk hole with a slot in it which is designed to hold the nib in place as the nut is tightened or loosened on the bolt.Flat Countersunk Nib Bolts are designed to sit flush on a surface.
They are commonly called Plow Bolts as they are often used to affix a blade to the edge of a plow.