Hans, Stainless Steel is used in a wide variety of underwater applications. Propeller shafts, rudders, rudder shafts, rudder ports, propeller cages, propeller struts, and the keel bolts which hold the ballast keel in place on sailboats. The bow thruster shaft, the very bolts which hold the bow thruster to the tube. Swim platform brackets and fasteners, and transom exhaust fittings. Many bronze powerboat rudders have a stainless steel shaft. Most marine ball valves have a stainless steel ball. These are just some of the many places you will find stainless steel in underwater applications. The use of stainless bolts with bronze seacocks is consistent with industry practice. Would bronze be better? Sure thing. But stainless is widely used today. I have excerpted some of this from an article I recently wrote on crevice corrosion, I can't share the entire article as I've sold the rights. "Stainless steel is iron alloyed with chromium and other metals: there are many different alloys of steel which are known as “stainless steel”:. The chromium allows the surface to undergo “passivation.” This is the formation of a surface film of chromium oxide. Passivated stainless steel is highly resistant to rust. However, it does rely on continual exposure to oxygen. In the air or free flowing water the ambient oxygen level is high enough to preserve the chromium oxide layer, and the metal will not rust. If the stainless is constantly submerged in water, particularly in saltwater, still water trapped against the stainless steel will be depleted of oxygen the passivation protection is lost and rust can begin. With higher water salinity the degradation of the passive layer is accelerated. As the corrosion starts, it creates a pit. The pit becomes a water trap to the free flow of water and so the immediate environment is not conducive to the return of a passive layer and the crevice corrosion is accelerated. One of the most frequently seen incidents of crevice corrosion is found on 304 stainless steel fasteners. Out of sight and out of mind, the corrosion here is often not seen until the fastener fails. Note: crevice corrosion is an entirely different corrosion process from galvanic corrosion. Adding a sacrificial anode will not prevent or correct crevice corrosion. Definitions · Stainless steel is an alloy of iron. o 304 stainless steel is 18-8. 18% chromium 8%nickel. Nickel increases resistance to corrosion. Nickel *may *make the 304-alloy nonmagnetic. o 316 stainless steel is 16-18% chromium, 10% nickel and 2-3% molybdenum. Molybdenum is added to the alloy to increase the resistance to corrosion in saltwater. 316 stainless is not magnetic. · Passivation: Chromium reacts with oxygen in the air and in the water to form a hard surface film which protects the steel and prevents oxidization (rust). After all machining and welding stainless steel parts are cleaned and degreased are submerged in ( usually) citric acid. The acid removes any exposed steel. The chromium and nickel on the surface combine with oxygen to for a tough but extremely thin chromium oxide layer which protects the surface from rust. " 316 stainless should be specified for any stainless steel used in salt water. It is important to understand the different alloys, although you cannot see the difference to the naked eye. 304 stainless will rust more freely than 316, but as new, it is very difficult to tell what alloy of steel you have. This raises a concern with stainless fasteners. 304 stainless can be (but is not always) magnetic. If you can detect that the fasteners are magnetic, then you have a very good reason to go back to the yard and request that the bolts be changed out to either bronze, or 316 stainless. In any event, I'd be sure to ask the boat yard to confirm that they specified 316 SS alloy for the bolts, (but I'm not certain they will.) Even if the bolts are 304 they will not fail catastrophically in short order. In any event, you will want to monitor them from time to time from inside the boat, and anytime the boat is hauled you want to look at the head of the bolts. If they are showing signs of rust, then one or more should be pulled and checked. In my career I designed, engineered and built boats, ran boatyards. I have seen examples of crevice corrosion. I've also seen "bronze" fittings fail. If the installer does not specify bronze, it is easy to confuse it with regular hardware store red brass fittings. Red brass plumbing fittings don't hold up well in salt water applications. Attached is a recent photo of a failed red brass fitting which was on a bronze seawater strainer. So If you are using bronze, be sure it really is bronze. So Hans, check to see if the bolts are magnetic. If so, they are 304 and should be replaced. If not, they might still be 304. Watch them for signs of rusting. And ask the yard to pull one for inspection the next time you have the boat hauled for bottom paint. If it is starting to rust, then ask for all the bolts to be replaced. Cheers, Tom Sanford, FL 410.212.7898