When rebuilding an old cultivator, or any old attachment for that matter, which grade is typically used for the general frame hardware bolts? I am working on an old Dearborn cultivator and I'm replacing most of the bolts due to rust as I make adjustments to it. I'm not refurbishing it, but getting it back into working order as a rusty old tool. These are bolts that hold bracing, the arms that hold the springs, and miscellaneous frame parts together. I've used a little bit of each grade during past projects but figured there must be a "right answer". The old bolts are too rusted to see any markings. So what's the best grade to use for holding an implement together but not subjected to extreme forces? Grade 2, 5, or 8?