Why is it recommended to install ASSY self-tapping screws in one continuous run?

Challenges with site access or equipment limitations may force the installer to stop and drive the ASSY screws in multiple runs.
If self-tapping screws are not installed in a single run, restarting the installation may introduce shear stresses that are not distributed uniformly along the length of the screw. This has a more critical effect in longer screws, where the installation needs to overcome considerable friction between the fastener and the wood. These additional driving stresses can result in premature fastener failure by screw breakage or by introducing pre-loading within the section.

The torque required to overcome the initial static friction is larger than the torque required to maintain the installation. There is also a risk that the driving hardware is not suitable to restart the installation, in addition to causing premature fastener failure.

It is highly recommended that ASSY screws be installed in one continuous run to prevent potential premature failures, since there is no way to do quality control on installed fasteners. If partial installation is required due to extraneous circumstances, it is recommended to pre-drill instead. Requirements and recommendations for pre-drilling ASSY fasteners can be found in the MyTiCon’s Structural Screw Design Guide.

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Relevant Technical Resources

Gallery esr 3178 ICC Code Approval ESR-3178 for Fully Threaded Screws (2018 revision)
Gallery canadian screw design guide cover Canadian Structural Screw Design Guide
Gallery dg   assy fastener catalog cover American Structural Screw Design Guide

Products Covered in this Article

Gallery assy eco explosion resized ASSY Eco Countersunk Head
Gallery assy sk explosion resized ASSY SK Washer Head
Gallery assy vg cyl explosion resized ASSY VG CYL Cylinder Head

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