A plow bolt is similar to a carriage bolt, except the head is flat or concave..The recess in the mating part must be designed to accept the particular plow bolt.
A hex key is required to tighten or loosen a socket screw. 1/4"-20 Socket Head Cap Screw, Black Chrome Plated Steel, 2-1/4 in Length, 4 PK. Socket screws are commonly used in assemblies that do not provide sufficient clearance for a conventional wrench or socket.