Most screws are made of steel, but the specific type of steel and the dozens of alternative materials available depend entirely on where the screw will be used. A wood screw holding together a bookshelf, a deck screw exposed to rain, and a surgical screw inside someone’s knee are made from very different stuff. Here’s what goes into each type and why it matters.
Carbon Steel: The Most Common Choice
The vast majority of screws you’ll find at a hardware store are carbon steel. This is an alloy of iron with roughly 0.05% to 2% carbon mixed in, plus trace amounts of other elements. The carbon content is what gives the steel its strength. Low-carbon steel is softer and easier to form into shape, while higher carbon content produces a harder, stronger screw that’s also more brittle.
Plain carbon steel screws rust quickly when exposed to moisture, so they’re almost always given a protective coating. Zinc plating is the most common, giving screws that familiar silvery or yellowish appearance. Black oxide and phosphate coatings are also used, particularly for drywall screws. These coatings slow corrosion but don’t eliminate it, which is why carbon steel screws are best suited for indoor use or dry environments.
Stainless Steel for Corrosion Resistance
Stainless steel screws contain at least 11% chromium, which reacts with oxygen to form a thin, invisible layer on the surface that resists rust. Within this category, there are several grades worth knowing about.
The most widely used is 304 stainless steel, sometimes called 18-8 because it contains about 18% chromium and 8% nickel. It handles everyday moisture, mild chemicals, and general outdoor exposure well, and it costs less than higher grades. For most home and commercial projects, 304 is the standard recommendation.
Grade 316 stainless steel steps things up with 16% chromium, 10% nickel, and 2% molybdenum. That added molybdenum is the key difference: it significantly improves resistance to chloride, the corrosive agent in salt. If you’re building near the coast, working around pools, or dealing with chemical exposure, 316 is the better pick.
There’s also the 400 series, which trades some corrosion resistance for greater hardness and heat tolerance. Grade 410, for example, has a higher carbon content and fewer alloying elements, making it stronger and better suited for high-temperature applications. You’ll find 400-series screws in engines, exhaust systems, and industrial equipment.
Brass and Bronze for Specialty Uses
Brass screws are an alloy of copper and zinc. They don’t rust, they’re easy to machine into precise shapes, and they conduct electricity well. You’ll see them in electrical terminals, decorative hardware, and antique furniture restoration where appearance matters. Brass is softer than steel, so these screws aren’t meant for heavy structural loads.
Silicon bronze is the go-to material for marine fasteners. It offers exceptional resistance to saltwater corrosion, outperforming even stainless steel in prolonged ocean exposure. Wooden boatbuilders have relied on silicon bronze screws for decades because they hold up in harsh saltwater conditions without degrading the surrounding wood the way some metals can.
Titanium and Surgical Screws
Titanium screws are roughly 40% lighter than steel yet remarkably strong, and the body tolerates them without triggering a significant immune response. This combination makes titanium the standard material for orthopedic screws used in bone fracture repair, spinal fusion, and joint reconstruction.
A newer alternative in surgery is PEEK, a high-performance plastic (polyether ether ketone) with mechanical properties that closely mimic natural bone. PEEK screws are increasingly used in ligament reconstruction. In a randomized trial of 133 patients who had ACL surgery, PEEK screws performed identically to titanium screws at the two-year mark. One practical advantage: PEEK doesn’t create the signal interference on MRI scans that metal implants do, making follow-up imaging much cleaner. Some surgical teams now prefer it for that reason alone.
Outside of medicine, titanium screws show up in aerospace, high-end cycling, and motorsport, anywhere saving weight without sacrificing strength justifies the higher cost.
Plastic and Nylon Screws
Nylon screws are lightweight, electrically insulating, and resistant to many chemicals. They won’t corrode, won’t conduct current, and won’t scratch delicate surfaces. Electronics manufacturers use them to mount circuit boards and components where a metal fastener could cause a short circuit. They’re also common in plumbing fixtures and laboratory equipment exposed to corrosive substances.
The tradeoff is mechanical strength. Nylon screws can’t handle the loads or temperatures that metal can, so they’re limited to light-duty applications.
Ceramic Screws for Extreme Environments
Alumina ceramic screws occupy a small but important niche. They’re electrically insulating, chemically inert against virtually every acid except hydrofluoric, and can withstand extreme heat. In semiconductor manufacturing and vacuum chamber equipment, ceramic screws solve problems that metal fasteners create, such as electrical arcing and material offgassing. They’re brittle compared to metal, so you won’t find them in applications involving impact or vibration, but in the right setting they’re irreplaceable.
How Coatings Change the Equation
The base material is only part of the story. Coatings can dramatically extend a screw’s lifespan or change its properties. Zinc plating is the most basic, adding a sacrificial layer that corrodes before the underlying steel does. Hot-dip galvanizing applies a thicker zinc coating, common on lag bolts and structural fasteners used outdoors. Ceramic-coated deck screws use a multi-layer finish that resists both corrosion and UV breakdown, often carrying warranties of 25 years or more.
Some screws are coated with a dry lubricant to reduce the torque needed to drive them, which matters in softwoods that split easily or in automated assembly lines where consistency is critical.
Recycled Content in Modern Screws
Steel screw production has shifted significantly toward recycled material. Nucor, one of the largest fastener steel producers in the U.S., reported that its steel products contained an average of 77% recycled content in 2023, with some product lines approaching 100%. Electric arc furnaces that melt down scrap steel now dominate domestic production, making the typical steel screw far less resource-intensive than it was a generation ago.
Choosing the Right Material
The material you need comes down to three questions: what forces will the screw handle, what environment will it live in, and does it need any special properties like electrical insulation or biocompatibility?
- Indoor furniture and framing: plain carbon steel with zinc plating
- Outdoor decks and fencing: coated carbon steel or 304 stainless
- Coastal or pool areas: 316 stainless steel
- Wooden boats: silicon bronze
- Electrical assemblies: nylon or brass
- Decorative hardware: brass or stainless steel
- High-heat industrial settings: 400-series stainless or ceramic
- Weight-critical engineering: titanium
Screw packaging typically lists the material and any coating, and structural fasteners carry grade markings stamped into the head that correspond to specific strength ratings defined by ASTM standards. If you’re buying screws for a load-bearing application, those markings tell you whether the fastener meets the mechanical requirements for the job.