1. Nothing, at least not necessarily. The typical fasteners found at most decent hardware stores (not the big boxes) tend to be National Fastener brand (in a blue and silver box), and these are declared as 304 SS alloy. 304 is acceptable, but not quite as corrosion resistant as 316. If the display or box doesn't declare a specific alloy, I'd be wary. I've never bought fasteners for a boat at a big-box store, and don't plan to ever start. I usually mail-order everything anyway, from sources that have quality fasteners.MikeD wrote:Hardware 101 questions:
1. What's wrong with plain old hardware store stainless fasteners?
Note that the 304SS fasteners that come from Bolt Depot are National Brand. I've used these plenty. You don't strictly need 316SS for all your fasteners, but it's the premium choice if you can.
2. Don't you dare ever use a zinc-plated fastener on your boat. They'll rust in a single season.MikeD wrote:2. What about the cheaper zinc plated fasteners? I'm guessing they corrode a lot faster than stainless?
Zinc-plated is a very different animal from hot-dipped galvanized, which one could argue might have a place on board in certain instances. Don't ever call zinc-plated "galvanized"; they're not galvanized, they're simply zinc-plated. The two processes are completely different, and offer completely different results. Keep the zinc plated fasteners for interior home use only.
Hot-dipped galvanized fasteners have been used in boat construction for a long time, particularly in working boats, mainly for cost reasons. They have an industrial look, and aren't as durable as stainless. The galvanizing process tends to leave lumps of the dull-gray zinc material in the threads and heads of fasteners. HD Galvanized fittings and fasteners have often been used for wooden boat fastening, and galvanized rigging wire is relatively common on "traditional" or working-type boats.
For certain uses on certain boats, hot-dipped galvanized material might be perfectly adequate, though if the coating becomes compromised (easy to do) the rust will set in rather quickly. But since most of your typical deck hardware is going to be stainless steel or bronze, it's best to stick with a similar metal for your fasteners.