It's a simple fact that it's the bolts in a body lift kit are the things that hold the cabin on to the chassis, so as you and your passengers sit in the cabin it's imperative that your vehicle body and chassis do not separate while you are doing your thing on the trail!
There are a couple of simple rules about using bolts and other fasteners for body lifts. Firstly regulations state that any modified component is at least as strong as the factory-fitted part. So if the manufacturer specifies a mild steel bolt (say 4.8 grade) and you select a high grade like 8.8, you will be perfectly safe if the nuts you choose have an interference fit to ensure they can't come loose.
By law, all bolts must have the grade marked on the head.
...you can use Nyloc nuts, or there are other solutions which can give you the same result, with metal to metal mating surfaces. Zinc plated bolts are often used with body lift kits because the fasteners are hidden away in places to protect them from rust.
And watch out for those thread pitches...
In Australia there are two standard thread pitches.
Yes, it is OK to use coarse thread bolts where possible, which is awesome because they are cheaper, but in situations where the bolts are screwed into an existing thread on your vehicle, there is a high possibility it will be a fine thread bolt.
When tightening up bolts during the installation of a body lift, you will find there is general guidance given for each bolt size pertaining to tightness in bolts with dry joints, for example in a body lift, and also where the bolts are lubricated, for example in a gear box... but it's safer to check the manufacturer's specifications around what "tight" actually means for your particular vehicle.
