The Simpson Strong-Drive SDHR Combo-Head Screw in 0.470 in. diameter and 4 in. length is a heavy-duty structural fastener engineered for mass timber construction, cross-laminated timber (CLT) assemblies, and general interior structural applications. Featuring a unique combination head that accepts both a T40 6-lobe driver bit and a 17-mm hex-head driver bit, this blue-zinc coated screw is built to pull structural members tightly together with excellent connection strength. The partially-threaded shank, knurled shaft, and Type-17 point work together to deliver fast starts and low-torque driving - making this fastener a reliable choice for engineered wood, factory-built construction, and steel-to-wood connections alike.

Key Features

• Combination Head (T40 6-Lobe or Hex-Head Drive) - accepts either a T40 6-lobe or 17-mm hex driver bit, giving installers flexibility to use the tools already on hand without switching hardware
• Blue-Zinc Interior-Grade Coating - provides corrosion protection suited for interior structural applications, helping maintain long-term connection integrity in mass timber and engineered wood assemblies
• Type-17 Point - designed for fast starts and low-torque driving, reducing installation effort and bit wear when driving into dense structural lumber or engineered wood products
• Knurled Shaft - the robust knurled section bites into surrounding material to resist pull-out forces, reinforcing the holding strength of the connection
• Partial Threading (2-1/8 in. Thread Length) - the partially-threaded design allows the screw to draw connected members firmly together rather than threading both pieces simultaneously, improving clamping action in structural joints
• 0.470 in. Outer Diameter / 0.315 in. Shank Diameter - the substantial outer diameter delivers structural-grade shear and withdrawal capacity suited for mass timber, CLT, and steel-to-wood connections
• 0.669 in. Head Diameter - the wide head provides a broad bearing surface that distributes load evenly, reducing the chance of pull-through in wood members
• 4 in. Length - deep penetration into structural members ensures strong, reliable connections across a range of timber thicknesses used in mass timber and modular construction
• Includes T40 6-Lobe Driver Bit - the required driver bit is included in the box, so installation can begin immediately without sourcing additional accessories

Why This Product

• Designed specifically for mass timber and cross-laminated timber construction - two of the fastest-growing structural building methods - this screw meets the demanding connection requirements of CLT panels and heavy engineered wood assemblies where standard fasteners fall short.
• The combination head eliminates the need to commit to a single driver style: whether a jobsite is set up with hex-head impact drivers or T40 6-lobe bits, this screw works with both - reducing downtime and tool changeovers during structural installation.
• The knurled shaft and Type-17 point work together to minimize cam-out and bit slippage during driving into dense timber, which translates to faster, more consistent installation and less wasted effort on each connection.
• Suitable for steel-to-wood, engineered wood, factory-built/modular construction, and mass timber applications - this single fastener covers a broad range of structural connection scenarios encountered in modern commercial and residential framing.

Specifications

• Brand: Simpson Strong-Tie
• Length: 4 in.
• Shank Diameter: 0.315 in.
• Head Diameter: 0.669 in.
• Thread Length: 2 1/8 in.
• Head Type: Combination
• Drive Type: T40 6-Lobe or Hex-Head
• Point Type: Type-17 Point
• Coating: Blue-Zinc Coated

Available Pack Options

• SDHR31400-R25: 25 Pk - includes T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)
• SDHR31400: 100 Pk - includes T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)

Approved Applications

• Steel-to-Wood/Engineered Wood
• Engineered Wood
• Factory-Built/Modular Construction
• Mass Timber / Cross-Laminated Timber

Install With

• Install using 6-lobe T40 or 17-mm hex-head driver bit

Frequently Asked Questions

What driver bits are compatible with the SDHR Combo-Head screw?

The combination head is designed to accept either a T40 6-lobe driver bit or a 17-mm hex-head driver bit. A T40 6-lobe driver bit is included in the box. The replacement bit part number for the included T40 bit is BIT40T-134-R2.

Is the blue-zinc coating suitable for outdoor or treated-lumber applications?

The blue-zinc coating on the SDHR Combo-Head screw is an interior-grade finish. It is intended for general interior structural applications, including mass timber and cross-laminated timber construction. It is not designated for exterior or pressure-treated lumber environments where a higher corrosion-resistance rating would be required.

What does the partial threading design do for structural connections?

The screw features a 2-1/8 in. thread length on a 4 in. overall length, making it partially threaded. This configuration is intentional - when driving into stacked structural members, the unthreaded shank passes through the near member while the threads engage only the far member, pulling both together tightly. This clamping action improves joint quality compared to fully-threaded designs in many structural connections.

What types of construction is this screw rated for?

The Strong-Drive SDHR Combo-Head screw in 0.470 in. diameter is designed for steel-to-wood and engineered wood connections, factory-built and modular construction, and mass timber and cross-laminated timber (CLT) assemblies. It is intended for general interior structural applications as described by Simpson.

Note: Product dimensions and/or thread length may differ from picture. Please see item description for specifications.