300 Series—austenitic chromium-nickel alloys
Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304.
Type 302—same corrosion resistance as 304, with slightly higher strength due to additional carbon.
Type 303—easier machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with International Organization for Standardization ISO 3506[6].
Type 304—the most common grade; the classic 18/8 stainless steel. Also referred to as "A2" in accordance with International Organization for Standardization ISO 3506[7].
Type 309— better temperature resistance than 304
Type 316—the second most common grade (after 304); for food and surgical stainless steel uses; Alloy addition of molybdenum prevents specific forms of corrosion. Also known as "marine grade" stainless steel due to its increased resistance to chloride corrosion compared to type 304. SS316 is often used for building nuclear reprocessing plants. Most watches that are made of stainless steel are made of this grade. Rolex is an exception in that they use Type 904L. 18/10 stainless often corresponds to this grade.[1] Also referred to as "A4" in accordance with International Organization for Standardization ISO 3506[8].
Type 321— similar to 304 but lower risk of weld decay due to addition of titanium

400 Series—ferritic and martensitic chromium alloys
Type 408—heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.
Type 409—cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
Type 410—martensitic (high-strength iron/chromium). Wear resistant, but less corrosion resistant.
Type 416— easy to machine due to additional sulfur
Type 420—"Cutlery Grade" martensitic; similar to the Brearley's original "rustless steel". Also known as "surgical steel". Excellent polishability.
Type 430—decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance.
Type 440—a higher grade of cutlery steel, with more carbon in it, which allows for much better edge retention when the steel is heat treated properly. It can be hardened to Rockwell 58 hardness, making it one of the hardest stainless steels. Also known as "razor blade steel". Available in three grades 440A, 440B, 440C (more common) and 440F (free machineable).