You should always use grade 8 bolts on an application like this. I changed out my 5/8" bolts to 3/4" frame bolts. The pin box had shifted so the air fill was touching the bottom of the overhang of the RV. The holes were punched 11/16" and that was too much slop so I drilled out as many as I could on each side to 3/4" so the bolts fit tight then tightened them to 200'# TQ.
