It's nice to get the proper bolts with the kit...
They can get pretty expensive fast if you have to buy them at the store... Grade 5 or grade 8...
Plus, sometimes the stores do not carry the perfect length, and then you have to determine if you can run the extra thread, or grind some down on a bench grinder so it doesn't bottom out in the hole before clamping the parts together...
You need to get the proper thread engagement for a good hold... Rule of thumb is 1 1/2 times the bolt diameter for the thread length... Example: If you have a 1/2" bolt, then you would want 1/2" + 1/4" = 3/4" of thread length to get a good clamp on the parts...