Simpson Strong-Drive SDHR Combo-Head Screw by Simpson is a heavy-duty structural fastener engineered for cross-laminated timber construction, mass timber construction, and general interior applications. At 6-1/4 in. long with a 0.390 in. outer diameter, this partially-threaded screw draws structural members tightly together while delivering excellent connection strength in demanding timber framing and wood-to-wood assemblies. The blue-zinc interior-grade coating, knurled shaft, and Type-17 point combine to make this fastener a reliable choice for mass timber and CLT projects where performance and ease of installation both matter.

Key Features

• Combination Head (T40 6-Lobe or 15-mm Hex) - the unique dual-drive design lets installers use whichever bit is on hand, reducing downtime and increasing job-site flexibility.
• Blue-Zinc Interior-Grade Coating - provides corrosion protection suited for interior structural applications, keeping the fastener secure and intact within finished assemblies.
• Type-17 Point - self-cutting tip bores into timber quickly for fast starts and low-torque driving, reducing installer fatigue during repetitive fastening tasks.
• Knurled Shaft - the robust knurled shank increases surface contact and grip within the wood, contributing to the high connection strength required in mass timber construction.
• Partial Threading with 4-3/8 in. Thread Length - threads engage only in the receiving member, allowing the screw to pull structural members firmly together rather than pushing them apart.
• 0.390 in. Outer Diameter / 0.275 in. Shank Diameter - a sturdy cross-section designed for structural load paths in heavy timber and CLT applications, providing reliable performance where connection integrity is critical.
• 0.590 in. Head Diameter - wider bearing surface distributes clamping load across the workpiece, reducing the risk of surface pull-through.
• Includes T40 6-Lobe Driver Bit - the included bit means the fastener is ready to install immediately, saving time sourcing accessories on the job site.

Why This Product

• Designed specifically for cross-laminated timber and mass timber construction - this screw addresses the demanding connection requirements of CLT panels and heavy structural members where standard wood screws fall short.
• The combination head eliminates the need to commit to a single driver bit type, giving crews with different tool setups the freedom to drive with either a T40 6-lobe or a 15-mm hex driver bit without swapping hardware.
• Partial threading is engineered to clamp structural members together rather than pushing them apart - a critical distinction in timber frame connections where joint integrity directly affects structural performance.
• The blue-zinc coated knurled shaft paired with the Type-17 point delivers fast, low-torque installation even in dense timber, making large-quantity structural fastening more efficient and less physically demanding.

Specifications

• Brand: Simpson Strong-Tie
• Length: 6-1/4 in.
• Head Type: Combination
• Head Diameter: 0.590 in.
• Shank Diameter: 0.275 in.
• Thread Length: 4-3/8 in.
• Drive Type: T40 6-Lobe or Hex-Head
• Point Type: Type-17 Point
• Coating: Blue-Zinc Coated
• Country of Origin: Taiwan

Available Pack Options

• SDHR27614-R25: 25 Pk - includes T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)
• SDHR27614: 100 Pk - includes T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)

Install With

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

Frequently Asked Questions

What applications is the SDHR Combo-Head screw designed for?

This screw is designed for cross-laminated timber construction, mass timber construction, and general interior applications. It is intended for use where structural members need to be pulled tightly together with excellent connection strength.

What driver bits are compatible with this screw?

The combination head accepts either a T40 6-lobe driver bit or a 15-mm hex-head driver bit. A T40 6-lobe driver bit is included with the screw. The replacement driver bit reference is BIT40T-134-R2.

Is this screw fully threaded or partially threaded?

This is a partially-threaded screw with a thread length of 4-3/8 in. The partial threading is designed so that the threads engage only in the receiving structural member, which pulls the members together rather than holding them apart - an important characteristic for structural timber connections.

Is this screw suitable for exterior or pressure-treated lumber applications?

The SDHR Combo-Head screw features an interior-grade blue-zinc coating, which makes it appropriate for general interior applications. It is not designated for exterior or pressure-treated lumber use.

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