See Stainless Steel Tolerances
Stainless Square Tube 304 Metric offers a great mix of strength and corrosion resistance in most situations outside of marine environments. If your project is in a marine environment, choose 316 stainless. 304, the most popular stainless alloy in the world, maintains its properties in high temperature situations. It is typically used in aerospace, food and beverage industry, pressure containers, architectural designs and trim, cryogenic applications, and chemical processing equipment.