Not all Hardware is the same. Much of the stuff you find at the local Hardware store won't make it through the season. Thats why all of the SS Hardware we sell is certified to be either 304, or 316 series stainless Steel. Our knife blades are even a proprieteray alloy imported from France.
We believe all primary tanks should be steel in order to be more negatively buoyant and reduce the need for lead weights. If it is a Stage / Bail-out bottle it should be aluminum. The advantage of aluminum 80, or an aluminum 40 is that it is close to being neutrally buoyant when filled and will not become positively buoyant until the tank pressure gets close to 500 PSI.