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.
It is known that 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 the 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 MTC Solutions’ Structural Screw Design Guide.
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