I have a question I hope someone with knowledge about Stainless Steel could answer for me. I have some SS washers with an inside diameter about 1/16" smaller than I want for a homemade weldless bulkhead I am installing. Are Stainless washer stainless through out or is it a coating like galvanized washers? Can I drill/grind the centers larger without rendering the Stainless open to staining and rust? If I can drill or grind them is there anything I should watch out for?