Barnes 4wd u-bolts are anything but standard! This u bolt measures 5/8" X 4 1/4" X 10". The biggest misconception with U-bolts is that they are all the same; this could not be farther from the truth. We feel that U-Bolts are the most important component of a leaf spring suspension and this is why we are so meticulous about the specifications of our U-bolts. Our U-bolts are made from a cold drawn 1541 alloy that is stress relieved. This produces an alloy that has grade 8 strength but not grade 8 hardness. The threads on our U-bolts are 5/8"-18 fine threads and are manufactured with a smooth rolled thread. The mating Hi-Nuts are hardened as well as the thick washers and are manufactured with sharp cut threads. When a U-Bolt is tightened the U-Bolt threads stretch as they mate with the Hi-Nuts. This insures proper tightness of the fastener is maintained. This stretching is not visible but a U-bolt should never be reused because removing the tall nut will cross thread the U-Bolt. Our U-bolts bolts have a torque spec of 150 foot pounds and should never be tightened with an impact gun.