That is really NOT inferior hardware per se. It is 304 SS and while 316 series is MUCH better, it is not the fault of the builder – but that of the marine hardware suppliers who make MOST items from 304 series. I’d guess 90% of the marine market uses 304 series. 316 series is passivated, thereby ensuring that there is a protective layer of molecules at the surface to protect the parent material. FWIW, when I bought special 316L hardware over 304, the price was 3X the price.
Solution: Remove and re-bed that hardware. I myself now put a piece of adhesive-lined heatshrink over the threads of any SS bolt or hardware, stopping just a tad over where the washer will contact it, as the washer will push it away & down so the nut can be torqued properly. Also NEVER over-torque SS hardware as that promotes “crevice corrosion”, where SS in particular has a nasty habit of ‘corroding’ faster when under tensile strain. FYI, I re-bedded all the deck/hull hardware on my ’92 when I first bought her in ’98 and my fittings don’t look like yours , so bedding the hardware works!
Your hardware and almost EVERY U-bolt I see on a hull shows some ‘staining’ due to the lack of oxygen to the threads inside the hull. Bedding the threads with Boatlife LifeCaulk or Seal or 3M 4200 will help minimize this, i.e., if the environment can’t get to it, it can’t or is less likely to stain.
