Simpson Strong-Drive SDCF TIMBER-CF Screw - 0.390 in. x 23-5/8 in. is a heavy-duty structural fastener engineered specifically for cross-laminated timber (CLT) construction, mass timber assemblies, and general interior structural applications. Manufactured by Simpson and finished with a yellow-zinc coating, this fully-threaded screw delivers the holding power and installation precision that demanding timber framing projects require. Its large flat head with underhead nibs and proprietary point geometry make it a purpose-built solution for high-performance wood construction where clean countersinking and reliable withdrawal resistance are non-negotiable.

Key Features

• 0.390 in. diameter structural shank - provides robust load-bearing capacity suited for mass timber and cross-laminated timber connections where structural integrity is critical
• 23-5/8 in. overall length with 23-3/8 in. thread length - nearly full-length threading maximizes thread-to-wood engagement, delivering excellent withdrawal resistance throughout the fastener's depth
• Flat head with underhead nibs - the 0.725 in. head diameter combined with nibs allows for clean, flush countersinking in timber surfaces without additional pre-drilling or surface preparation
• T50 6-Lobe drive type - provides a positive, cam-out-resistant drive interface that reduces bit slippage and speeds up installation in dense timber materials
• Proprietary unique point geometry - enables fast, accurate starts in thick timber without pre-drilling, saving labor time on the job site
• Yellow-zinc fully-threaded coating - the yellow-zinc finish provides corrosion resistance appropriate for interior and dry application environments, keeping fasteners protected throughout the service life of the structure

Why This Product

• Designed specifically for cross-laminated timber (CLT) and mass timber construction - this screw addresses the unique fastening demands of engineered wood panels and heavy timber assemblies where standard fasteners fall short
• The combination of a proprietary point and near-full-length threading means fast installation starts and maximum withdrawal resistance - reducing installation time while maintaining structural performance in thick timber sections
• The large flat head with underhead nibs countersinks cleanly into timber surfaces - eliminating unsightly raised heads and providing a finished, professional appearance in exposed mass timber applications
• At 23-5/8 in. in length, this fastener is built for the deep penetrations required in thick CLT panels and mass timber members - giving structural engineers and contractors the reach needed for code-compliant connections

Specifications

• Brand: Simpson Strong-Tie
• Length: 23-5/8 in.
• Shank Diameter: 0.290 in.
• Head Diameter: 0.725 in.
• Thread Length: 23-3/8 in.
• Head Type: Flat Head with Nibs
• Drive Type: T50 6-Lobe
• Coating: Yellow-Zinc Coated
• Finish: Yellow-Zinc Coated
• Country of Origin: Austria

Available Pack Options

• SDCF272358-R25: 25 Pk - includes one T50, 6-lobe driver bit (replacement bit: BIT50T-2-R1)
• SDCF272358: 100 Pk - includes two T50, 6-lobe driver bits (replacement bit: BIT50T-2-R1)

Approved Applications

• Cross-laminated timber (CLT) construction
• Mass timber construction
• General interior structural applications
• Interior and dry environments only

Frequently Asked Questions

Is this screw suitable for outdoor or wet applications?

No. The Strong-Drive SDCF TIMBER-CF screw with yellow-zinc coating is designed for interior and dry applications only. It is not rated for exterior, wet, or treated-lumber environments where higher corrosion resistance would be required.

Does this screw require pre-drilling before installation?

No pre-drilling is required. The proprietary unique point geometry is engineered to provide fast starts and accurate penetration into timber materials without pilot holes, streamlining the installation process on mass timber and CLT projects.

What drive bit is needed for the SDCF TIMBER-CF screw?

This screw uses a T50 6-Lobe drive interface. A T50 6-Lobe bit is required for installation. The 6-Lobe design helps prevent cam-out during driving, which is especially beneficial when installing long fasteners into dense timber members.

What is the difference between the shank diameter and the listed 0.390 in. diameter?

The 0.390 in. diameter refers to the major (thread) diameter of the screw - the outer diameter measured across the threads. The shank diameter of 0.290 in. is the narrower unthreaded core portion. Both measurements are relevant when specifying fastener clearances and load values for structural timber connections.