Stainless is a series of alloy steels which contain at least 12% chromium. Such steels will not rust when exposed to weather. The most common stainless steel is 304 which is an 18-8 alloy containing at least 18% chromium and 8% nickel. 304 is a non magnetic steel. The metric designation for 304 is A-2. Even more corrosion resistant alloys, such as 316, are available for some of our product line and are a good choice for high corrosion environments such as marine use. We carry medium strength hex and socket head cap screws made from strain hardened 316 in metric sizes. These fasteners have a strength designation of 80 and are approximately equivalent to metric 8.8 or a US grade 5. We have an extensive line of high strength stainless as strong as or stronger than US grade 8. The high strength bolts are made from age or precipitation hardened stainless and have a polished finish.
Stainless steel is superior to chrome plating because it won't crack or peel as it isn't a surface coating but the substance from which the fastener is made. Because stainless steel is softer than medium carbon steels (it only seems harder because it work-hardens) it tends to gall. Always use anti-Seize or a similar product on the threads.