A fastener in construction is any hardware device used to connect two or more structural members together. That includes everything from the nails holding drywall to wood studs, to the high-strength bolts joining steel beams in a bridge. Fasteners are one of the most fundamental components on any job site, and the right choice depends on the materials being joined, the loads involved, and the environment the connection will face.
How Fasteners Work: Threaded vs. Non-Threaded
Construction fasteners fall into two broad mechanical categories. Threaded fasteners, like bolts and screws, grip materials by pulling them together along spiral grooves cut into the shaft. Non-threaded fasteners, like pins and rivets, hold materials in place through friction, mechanical interlock, or by physically deforming to fill a hole.
Bolts are always used with a nut on the opposite side, clamping two elements tightly together. They’re the go-to choice when a connection needs to resist shear forces (loads pushing sideways) and bending forces. Screws, by contrast, thread directly into the material itself, which makes them the workhorse of wood and light-gauge metal construction. Pins allow rotational movement between connected parts, which is useful in machinery and certain structural joints. Riveted connections were once the standard for steel construction but have largely been replaced by welding and high-strength bolting.
Common Fastener Types by Application
Structural Steel Bolts
Heavy steel construction relies on two main bolt grades. Grade A325 bolts, made from medium carbon steel, have a minimum tensile strength of 120,000 PSI for diameters of one inch or less. They’re the standard choice for bridge and highway projects and can be galvanized to resist corrosion, which makes them practical for outdoor infrastructure. Grade A490 bolts are stronger, rated at 150,000 PSI minimum tensile strength, but they come with trade-offs: they cannot be galvanized and are more susceptible to stress corrosion cracking. That vulnerability means A490 bolts see less use in bridges and highways despite their higher strength.
Wood and Drywall Fasteners
For wood framing and drywall, nails and screws come in specialized designs matched to the material. Drywall nails feature a ringed or barbed shank that increases holding power compared to a smooth nail. Cement-coated nails use a resin coating on a smooth shank to achieve a similar grip. Cupped-head nails have a rounded head that’s easier to countersink for a flush finish.
Drywall screws are more common than nails today. Coarse-thread screws attach drywall to wood studs, while fine-thread screws with smaller heads are designed for metal studs. Most drywall screws are self-starting, meaning their sharp, hardened tips can drive directly into the material without a pilot hole. For 1/2-inch drywall panels, you’d typically use 1-1/4 or 1-3/8-inch screws. For thicker 5/8-inch panels, 1-3/8 to 1-5/8-inch screws are standard.
Self-Drilling and Self-Tapping Screws
These two types sound similar but serve different purposes. Self-drilling screws have a drill-point tip that bores its own pilot hole and cuts threads in a single step, making them ideal for attaching roofing panels, sheet metal, and other materials where speed matters. Self-tapping screws can cut or form their own threads but still require a pre-drilled hole. Some self-tapping designs have flutes at the tip for clearing metal chips, while thread-forming versions create threads by pushing the material aside rather than cutting it. For harder metals like steel, self-tapping screws work best in thinner gauges.
Concrete Anchors
Fastening anything to concrete requires a completely different approach, since you can’t drive a screw into solid concrete the way you would into wood. Mechanical anchors are installed into pre-drilled holes and grip the concrete through expansion. When you tighten the bolt, a sleeve inside the hole expands outward, creating friction and mechanical interlock against the concrete walls. These are commonly used to attach structural elements to beams, columns, and slabs.
Chemical anchors use an epoxy or resin that bonds a threaded rod directly to the concrete. They handle the highest static loads and are often the better choice for dynamic applications, including structures in earthquake zones. Chemical anchors can even work in wet or flooded holes without losing performance. The main limitation is temperature: standard epoxy anchors generally shouldn’t be installed below 5°C (41°F), though winter-grade formulas with faster curing times are available for cold environments.
Shear, Tension, and Combined Loads
Every fastener in a structure deals with one or both of two basic forces. Tension pulls the fastener along its length, trying to pull it apart. Shear pushes sideways across the fastener, trying to slice through it. Many real-world connections subject fasteners to both forces simultaneously, and the combined load has to fall within the fastener’s total capacity for the connection to be safe.
Where the load hits the fastener matters too. A bolt loaded along its smooth, unthreaded shank is significantly stronger than the same bolt loaded across its threaded section, because the threads reduce the cross-sectional area and create stress concentration points. This is why structural engineers specify bolt lengths and installation methods that keep the shear plane on the shank rather than the threads whenever possible. In connections with very thick materials or shims, the offset between joined pieces can also introduce bending forces on the fastener, further complicating the load picture.
Coatings and Corrosion Protection
A fastener’s material and coating determine how long it lasts in a given environment. Unprotected steel corrodes quickly when exposed to moisture, so nearly all construction fasteners receive some form of surface treatment.
Zinc-based coatings are the most common because zinc does more than just form a physical barrier. When the coating gets scratched or cut, exposing bare steel underneath, the zinc corrodes sacrificially instead. Zinc is more chemically reactive than steel, so it gives up its own material to protect the steel beneath it. This is called galvanic protection, and it’s the reason zinc coatings outperform simple paint or lacquer in the long run.
The specific coating method determines the thickness and durability of that zinc layer:
- Phosphate coating: The black or gray finish found on most drywall screws. It’s the lowest-cost option, offering only minimal protection suitable for dry indoor use.
- Electro-zinc plating: The most common fastener finish overall. Zinc is electroplated onto the steel at a thickness of about 4 to 8 microns, then sealed with a clear or yellow coating for additional protection.
- Mechanical zinc plating: Powdered zinc is pounded onto the fastener surface using glass beads in a tumbling process, producing coatings from 5 to 25 microns thick. Thicker coatings mean better corrosion resistance.
- Hot-dip galvanizing: Fasteners are dipped in molten zinc, producing the thickest and most durable coating. However, the process isn’t common for fasteners because the thick zinc layer can interfere with threads on smaller hardware.
For the most demanding environments, like coastal or marine construction, stainless steel fasteners skip the coating question entirely. Stainless steel alloys are inherently corrosion-resistant, making them the preferred choice where salt exposure, high humidity, or chemical contact would overwhelm zinc-based protection.
Choosing the Right Fastener
Selecting a construction fastener comes down to four practical questions: what materials are you joining, what forces will the connection face, what environment will it live in, and what building codes or engineering standards apply. A wood-to-wood connection in a dry interior wall has completely different requirements than a steel beam splice on an exposed bridge deck. Getting the material, grade, size, and coating right isn’t just a matter of performance. It’s a structural safety requirement governed by engineering standards from organizations like ASTM, which set specifications for everything from the steel alloy in a bolt to the thickness of its zinc coating.
On a practical level, the best approach is to match the fastener to the weakest link in the connection. There’s no benefit to using a 150,000 PSI bolt if the material it’s threaded into can’t handle that load, and an expensive stainless steel screw is wasted in a climate-controlled interior. The goal is a connection where the fastener, the materials, and the environment are all in balance.