To the layperson, wood is wood, metal is metal, that's as far as it goes. The average person may not understand why Cedar is a good choice for outdoor furniture or Oak makes for a hardy floor. Ditto with the various types of metals. Stainless steel, particularly in the EDC market, is often cited along with a number, meant as shorthand to express the benefits of that particular grade. Do ordinary consumers know the difference?Here I'll break down the stainless steel grades that you're most likely to see in product design or architectural applications. This isn't a comprehensive list, but something that industrial designers should at least be able to explain to their clients.The first number of a stainless steel grade denotes which general category it's in, and the second two numbers indicate the specific ingredient blend, which influences the material's properties.300 Series, AusteniticStainless steels in the 300 grade are the most widespread. They've got excellent corrosion resistance. They've got excellent ductility, meaning the material can be shaped and deformed without cracking. And they are not magnetic.304 Stainless SteelPerhaps the most common type you'll see, as it's easy to form and weld. You'll see it in kitchen sinks, elevator doors, hospital furniture, architectural panels and handrails. It's food-grade, so they make commercial kitchens out of the stuff. 316 Stainless Steel This one ups the already-good 300 series' corrosion resistance to marine-grade. You'll find it on boat fittings, as well as architectural panels and outdoor handrails in coastal areas. It's also bio-compatible, so you can make orthopedic implants out of it. Like 304, it's food-grade. 303 Stainless Steel Similar to 304, but modified with a splash of sulfur to make it better for machining. It's the stuff that non-magnetic screws and bolts are made of. 400 Series, FerriticThe 400 series in the Ferritic subcategory are magnetic, and offer just moderate corrosion resistance compared to the 300 series. They're also less expensive.430 Stainless Steel Basically a lesser, magnetic version of 304. You'll see it in architectural panels, but typically interior only (remember, it's less corrosion-resistant than the 300 stuff). An expensive truck fender might be made of 304, and the manufacturer might offer a step-down model made of 430; the latter will require regular preventative maintenance to avoid corrosion. Interestingly, some manufacturers claim 430 is food-grade, while others disagree. That said, you can easily find commercial kitchen equipment made of the stuff.Top, more expensive 304. Bottom, more affordable 430.409 Stainless Steel This is what the exhaust system on your car is made out of. You use 409 when you have an application that requires heat resistance. 444 Stainless Steel Above we'd mentioned that 316 is the go-to for marine environments. If your client just doesn't have the budget (or if the application really needs to be magnetic), you can step down to 444, which is cheaper and still able to deal with moderate marine environments. You'll also see this in architectural panels in coastal applications, where 316 might've been more desirable, but the scale of the project made 444 more financially feasible. 400 Series, MarseniticThese are 400 series materials that have been heat-treated, endowing them with high strength and wear resistance.410 Stainless Steel You'll find these in kitchen cutlery, utensils, and fasteners where magnetism is desirable. You'll find a lot of self-tapping screws are made of 410, as the heat-treating gives them the strength required to drive through the part. 420Basically more expensive 410, with some trade-offs. It's got more carbon, making it harder and more wear-resistant than 410, but it's also less ductile and can be brittle after hardening; your manufacturer really has to know what they're doing. It's harder to machine and weld, and will thus bring higher manufacturing costs. You'll find this stuff in surgical instruments and high-quality knives. If an EDC person with some prized specialty knife is bragging about the material, it's likely 420.Beyond these basic grades you can get into Duplex stainless steels, which combine the properties of austenitic and ferritic steels, and Precipitation-Hardening (PH) stainless steels. These expensive variants are more likely to be used in offshore drilling rigs or aerospace applications, and are probably beyond your average industrial designer's needs. However, if you've worked with these exotics, please let us know your experience in the comments!