304 Stainless vs 316 Stainless Bolts, Screw, and Nuts - How Do They Differ?

There are various stainless steel alloys used in fasteners, but the most common are 304 and 316. 

The main alloying element in stainless steel is chromium. In fact, to be considered a true stainless steel, an alloy must contain a minimum of 10.5% chromium as it is the primary factor in what makes stainless “stain less.” 

304 stainless steel has approximately 18% chromium. It is often called “18-8” because it contains 18% chromium and 8% nickel (approximately).

316 stainless steel has about the same amount of chromium as 304 but adds more nickel and more molybdenum, increasing its overall corrosion resistance. 

Both 304 and 316 are in the category of stainless known as Austenitic which refers to the molecular structure. Stainlesses in this series (300 series) are high in chromium and nickel. Contrast that with 400 series stainless steels which are known as Martensitic and have a higher proportion of carbon. With their higher carbon content, 400 series stainless steels tend to be stronger, harder, and less ductile than 300 series stainless steels.