The Simpson Strong-Drive SDCF Timber-CF Screw (0.315 in. diameter x 8-5/8 in. length) is a heavy-duty structural fastener engineered specifically for cross-laminated timber (CLT) construction, mass timber assemblies, and general interior structural applications. Yellow-zinc coated for corrosion resistance in dry environments, this fully-threaded screw delivers exceptional withdrawal resistance and clean installation thanks to its flat head with underhead nibs and proprietary point design - making it a dependable choice wherever high-strength timber fastening is required.

Key Features

• 0.315 in. shank diameter with full threading - provides deep thread engagement throughout the entire fastener length, maximizing withdrawal resistance in mass timber and CLT connections
• Flat head with underhead nibs - the nibs score the wood surface as the screw seats, enabling clean, flush countersinking without pre-drilling for a finished, professional result
• T40 6-Lobe drive type - the high-torque 6-lobe interface reduces cam-out during installation, keeping the bit engaged even under heavy driving loads in dense timber materials
• Yellow-zinc coating and finish - protects against oxidation during storage and interior use, maintaining fastener integrity in dry, interior structural environments
• Proprietary unique point design - enables fast starts without pre-drilling pilot holes, reducing installation time in demanding CLT and mass timber applications
• 8-5/8 in. total length with 8-1/4 in. thread length - the long thread engagement is optimized for the thick panel-to-panel and panel-to-framing connections common in mass timber construction
• 0.590 in. head diameter - the wide bearing surface distributes clamping load over a larger area, reducing the risk of pull-through in structural wood panels

Why This Product

• Engineered specifically for cross-laminated timber and mass timber construction - where standard wood screws lack the shank diameter, thread geometry, and length required for code-level structural connections
• Fully threaded from tip to head - unlike partial-thread screws, the complete thread engagement along all 8-1/4 in. of thread length means the fastener pulls and holds through the full depth of the connection, delivering uncompromised withdrawal resistance
• The flat head with nibs eliminates the need for a countersink bit in most applications - the nibs self-recess on contact, saving labor steps during high-volume CLT panel installation
• The T40 6-lobe drive reduces bit slippage and stripped drives - a practical advantage when setting dozens of structural screws overhead or at difficult angles in timber framing work

Specifications

• Brand: Simpson Strong-Tie
• Coating: Yellow-Zinc Coated
• Finish: Yellow-Zinc Coated
• Drive Type: T40 6-Lobe
• Head Type: Flat Head with Nibs
• Head Diameter: 0.590 in.
• Shank Diameter: 0.230 in.
• Length: 8-5/8 in.
• Thread Length: 8-1/4 in.
• Country of Origin: Austria

Available Pack Options

• SDCF22858-R50: 50 Pk - includes one T40, 6-lobe driver bit (replacement bit: BIT40T-134-R2)
• SDCF22858: 250 Pk - includes two T40, 6-lobe driver bits (replacement bit: BIT40T-134-R2)

Approved Applications

• Cross-laminated timber (CLT) construction connections
• Mass timber structural assemblies
• General interior structural wood fastening applications
• Interior and dry-condition installations only

Frequently Asked Questions

Is the SDCF Timber-CF screw suitable for outdoor or wet applications?

No. The yellow-zinc coated SDCF screw is designed for interior and dry applications only. It is not rated for exterior, exposed, or high-moisture environments. For outdoor or wet-service applications, a different fastener with appropriate corrosion protection would be needed.

Does this screw require a pilot hole before installation?

In most cases, no. The proprietary unique point on the SDCF Timber-CF screw is designed to provide fast starts and self-drilling entry into timber, eliminating the need for pilot holes in typical CLT and mass timber applications. This speeds up installation significantly on large-scale timber projects.

What drive bit is required for the SDCF Timber-CF screw?

This screw uses a T40 6-Lobe drive. A T40 Torx-style bit is required for installation. The 6-lobe interface is specifically chosen to handle the high torque needed when driving a 0.315 in. diameter structural screw into dense timber without cam-out.

Why does this screw have a fully threaded shank rather than a partial-thread design?

The fully threaded design - with 8-1/4 in. of thread along the 8-5/8 in. total length - maximizes withdrawal resistance along the entire depth of the connection. In mass timber and cross-laminated timber applications, full thread engagement is critical for achieving the structural holding values required by these demanding assemblies.