The original bolts were grade 5s, but I always replace everything /w grade 8s. (its not like these bolts hold the rear axle under it or anything). To the best of my memory, the shackle bolts have 7/8" heads, which means they are 5/8" bolts. The bolts that go through the spring eyes have 15/16" heads, so they are 11/16" bolts. Im not totally sure on these, its been a few months, hopefully someone else will confirm.