bronze or stainless... for thru-hull, cleats, etc.

[Bushwacker]

Unless you use Monel (nickle-based alloy), you'll get crevice corrosion on even the best stainless. It needs exposure to oxygen to keep it "stainless", so where it's exposed to moisture but no air, you can get some pretty serious corrosion. That's why the big boats use bronze for stuffing boxes, seacocks and through-hull fittings, etc.