GRADE 8 PLOW BOLTS: Plow bolts have a slightly beveled head with a square neck under the head. The square neck sits in a prefabricated square hole in the steel. This keeps the bolt from turning as a nut is tightened on to the bolt. A Grade 8 bolt has a greater tensile strength than Grade 5 and Grade 2 bolts. They are designed for use in high stress applications. The length of a Plow bolt is determined by measuring from under the head of the bolt to the base of the threads.