Structural Screw Guide: Types & Applications

What Are Structural Screws?

Structural screws are engineered fasteners designed specifically for load-bearing structural connections in construction. Unlike standard screws, which are designed for general fastening, structural screws are manufactured to meet specific engineering standards and provide published load values that building codes require for structural connections.

Structural screws offer several advantages over traditional lag bolts and structural nails. They're self-tapping, eliminating the need for pre-drilling in most applications. They feature specialized thread designs that provide superior holding power. And they're available in a wide range of lengths and diameters for various structural applications.

The most popular structural screw brands include GRK (RSS, R4, and LedgerLOK), FastenMaster (HeadLOK and ThrULOK), and Simpson Strong-Tie (Strong-Drive). Each manufacturer offers screws with specific features and engineering data. At Fastener Express, we primarily stock GRK structural screws, which are the most widely used and specified structural screws in construction.

Types of Structural Screws

• GRK RSS: Rugged Structural Screws for general structural connections
• GRK LedgerLOK: Specifically engineered for deck ledger board connections
• GRK R4: Multipurpose screws for general construction fastening
• GRK Fin/Trim: For finish applications requiring screw holding power
• FastenMaster HeadLOK: For heavy-duty structural fastening
• FastenMaster ThrULOK: For through-bolt replacement applications
• Simpson Strong-Drive: Structural screws for use with Simpson connectors

GRK RSS Structural Screws

GRK RSS (Rugged Structural Screw) is the most popular structural screw in construction. These screws are used for a wide range of structural applications including framing connections, multi-ply beam fastening, post-to-beam connections, ledger board attachment, and pole barn post laminating. They're available in lengths from 2.5 inches to 12 inches, accommodating a wide range of material thicknesses.

RSS screws feature a specialized washer head that eliminates the need for separate washers. The integrated washer head distributes load across a larger area, reducing the risk of pulling through the material while providing a clean, finished appearance. The self-tapping tip eliminates pre-drilling in most applications, and the thread design provides superior withdrawal resistance compared to lag bolts.

RSS screws are available with GRK's proprietary Climate coating, which provides excellent corrosion resistance for interior and most exterior applications. For coastal areas or applications with constant moisture exposure, GRK offers Pheinox (stainless steel) versions of many RSS sizes. Climate coating is compatible with ACQ and copper azole treated lumber.

GRK LedgerLOK for Deck Ledger Connections

The deck ledger board connection is one of the most critical connections in residential construction — a failed ledger connection can cause a deck to collapse. Building codes now require specific fastening methods for ledger board connections, and the GRK LedgerLOK screw is specifically engineered to meet these requirements.

LedgerLOK screws feature a washer head design that meets code requirements for deck ledger connections. They provide published load values that building inspectors require for code compliance. The screws are self-tapping, eliminating the need for pre-drilling, and they install much faster than through-bolts or lag bolts — the traditional alternatives for ledger connections.

For deck ledger connections, the number and spacing of LedgerLOK screws depends on the joist spacing, ledger size, and local building code requirements. The IRC provides tables that specify fastener patterns for ledger connections. Our team can help you determine the right number and spacing of LedgerLOK screws for your specific deck configuration.

Choosing the Right Structural Screw

Selecting the right structural screw depends on the application, the materials being fastened, the required load capacity, and the environmental conditions. For general structural connections like multi-ply beam fastening and post-to-beam connections, GRK RSS screws in appropriate lengths are typically the best choice. For deck ledger connections, LedgerLOK screws are specifically engineered for the application.

Screw length should be selected based on the total thickness of the materials being fastened, plus adequate thread engagement in the receiving member. A general rule is that the screw should penetrate at least 2 inches into the receiving member for structural connections. Our team can help you calculate the right screw length for your specific application.

For applications requiring building code compliance, always check the manufacturer's published load values. These values specify the allowable loads for specific screw sizes in specific wood species and connection configurations. Building inspectors may require this documentation for permit approval and final inspection.

Installation Tips for Structural Screws

While structural screws are self-tapping and don't require pre-drilling in most applications, there are exceptions. For hardwoods and dense materials, pre-drilling may be needed to prevent splitting. For applications near board ends or edges, pre-drilling can prevent splitting. The pre-drill hole should be slightly smaller than the screw shank diameter.

Structural screws should be driven with an impact driver rather than a standard drill. The impact driver's higher torque and concussive action make driving large structural screws much easier and faster. Use a quality driver bit (typically star/Torx drive for GRK screws) that matches the screw head precisely to prevent stripping.

Don't overdrive structural screws. Drive them until the washer head is snug against the material surface, but don't continue driving beyond that point. Overdriving can strip the threads, damage the material, or break the screw. For critical structural connections, the manufacturer's installation instructions specify the proper installation procedure and any torque requirements.