The Simpson Strong-Drive SDHR Combo-Head Screw is a heavy-duty structural fastener engineered for cross-laminated timber construction, mass timber assemblies, and general interior applications. Built with a partially-threaded shank and a robust 0.390 in. outer diameter, this blue-zinc coated screw is purpose-built to draw structural members tightly together while delivering exceptional connection strength in engineered wood and modular construction settings. The unique combination head design accepts both a T40 6-lobe driver bit and a hex-head driver bit, giving installers the flexibility to use the tools already on hand - reducing setup time and keeping work moving efficiently.

Key Features

• Combination Head (T40 6-Lobe or Hex-Head Drive) - accepts either a T40 6-lobe bit or a 15-mm hex-head bit, so installers are never locked into a single driver type on the job site
• Blue-Zinc Interior-Grade Coating - provides corrosion resistance appropriate for interior and protected general applications, keeping the fastener performing reliably in mass timber and engineered wood environments
• Type-17 Point - designed for fast starts and low-torque driving, reducing the effort needed to begin each fastening and minimizing the risk of wood splitting
• Knurled Shaft - the robust knurled shank improves grip and pull-through resistance, helping structural members stay firmly drawn together over time
• Partially Threaded Design with 2-1/8 in. Thread Length - thread engages only the receiving member, allowing the screw to clamp structural layers firmly together rather than pushing them apart
• 0.590 in. Head Diameter - a wide bearing surface distributes load effectively across the connection point, supporting strong and stable structural joints
• 4 in. Overall Length with 0.275 in. Shank Diameter - sized for deep penetration into mass timber and engineered wood members, providing the embedment depth needed for high-strength connections
• Includes T40 6-Lobe Driver Bit - the matching driver bit ships with the product so installation can begin immediately without sourcing additional tooling

Why This Product

• Designed specifically for cross-laminated timber and mass timber construction - two of the fastest-growing structural building methods - making this screw a directly applicable fastener for modern wood structural systems rather than a generic retrofit
• The combination head eliminates the need to have a single specific driver bit on hand; whether you reach for a hex driver or a T40 6-lobe bit, the screw drives reliably, reducing downtime and tool swaps in fast-paced construction environments
• The Type-17 point and partially-threaded shank work together to enable fast, low-torque driving that pulls members tight without pre-drilling in many applications - keeping installation efficient in engineered wood and factory-built construction projects
• Blue-zinc coating delivers interior-grade corrosion protection suited to factory-built, modular, and protected mass timber applications where consistent fastener performance is critical to structural integrity

Specifications

• Brand: Simpson Strong-Tie
• Coating: Blue-Zinc Coated
• Length: 4 in.
• Head Diameter: 0.590 in.
• Shank Diameter: 0.275 in.
• Thread Length: 2 1/8 in.
• Head Type: Combination
• Drive Type: T40 6-Lobe or Hex-Head
• Point Type: Type-17 Point
• Country of Origin: Taiwan

Available Pack Options

• SDHR27400-R25: 25 Pk - includes T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)
• SDHR27400: 100 Pk - includes T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)

Approved Applications

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

Install With

• Install using 6-lobe T40 or 15-mm hex-head driver bit

Frequently Asked Questions

What makes the combination head design useful on a job site?

The combination head accepts either a T40 6-lobe driver bit or a 15-mm hex-head driver bit. This means installers working in cross-laminated timber or mass timber applications are not limited to a single driver type - they can use whichever compatible bit is already available, reducing tool changes and keeping work moving efficiently.

Is this screw suitable for exterior or exposed applications?

The SDHR Combo-Head screw features an interior-grade blue-zinc coating, which means it is designed for interior and protected general applications such as mass timber, engineered wood, and factory-built construction. It is not rated as an exterior or weather-exposed fastener based on its coating specification.

Why is a partially threaded design used for structural timber connections?

A partially threaded shank - with 2-1/8 in. of thread length on this 4 in. screw - means the threads engage only the receiving structural member. The unthreaded shank portion passes through the first member freely, allowing the screw head to bear down and clamp both members tightly together. This is critical for structural connections in cross-laminated timber and mass timber assemblies where tight member contact is required for connection strength.

What is the Type-17 point and why does it matter?

The Type-17 point is a cut-thread tip design that bores into wood fibers as the screw is driven, enabling fast starts and low-torque driving. In practical terms, this means the screw begins penetrating engineered wood or mass timber more easily and with less resistance, which reduces fatigue during installation and lowers the likelihood of wood splitting at the entry point.

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