As a side note

Using grade 8 bolts will in some cases allow you to use smaller sizes , thusly saving weight

Farm & Fleet sell grade 8 in bulk by weight, so if your near something similar you can buy all your nuts and washers plus several more commonly used bolts for what just a few would cost at a hard ware store

And an airbag is lighter than a beer belly for crash protection so use the grade 8.