Plow bolts feature a countersunk, flat head, square neck, and unified thread pitch. They are commonly used in road graders, scoop shovels. Or other heavy-duty industrial equipment whereas a flat, smooth surface is required. For flat heads of plow bolts, length is measured from the top of the head to the threaded end of the bolt. For dome heads, measure length from the largest diameter point of the head where the dome top meets the conical bearing surface) to the extreme end of the bolt. The size of the head varies with the size of the bolt.
The plow bolt is a flush-fitting carriage bolt, because its head is countersunk beneath the surface of the wood. Hence it was devised to hold replaceable plowshares to the muldboards of iron plow. Moreover the fastest-wearing part of the bolt, would be replaced several times over the life. Such bolts continue to be used to hold shovels onto cultivators. A bolt that has a conical head with a flat top and a smaller square shank below the head to keep the bolt from turning as its nut is tightened. Such bolts are used to hold parts of the plow together that have scouring surfaces. The bolt head fits into a conical hole sized so that the top of the head is flush with the scouring surface. If a bolt with a conventional head were used, the head would prevent good scouring and would eventually wear away.