Gee! For the extra buck or two it will cost I would go with grade 8 bolts. They are ready available at the local hardware store and will also have chromate finish in addition to the zinc or cad for improved corrosion protection compared to the typical grade 5.
Grade 5 bolts have three radial lines stamped on the head, a grade 8 will have 6 lines. A grade 8 is 50% stronger than a grade 5.
I use grade 8 for everything that supports weight or fastens something that moves.
