Steel is part of the fastening system
A screw connection cannot be assessed from the fastener alone. The connected steel provides the material into which the thread engages and often controls the governing failure mode. Thickness and mechanical strength therefore influence both installation behaviour and connection resistance.
Effect of steel thickness
Increasing the thickness of the member receiving the thread generally increases the available engagement depth. This can improve pull-out resistance, but only while the screw geometry and installation remain suitable. For self-drilling screws, increasing thickness also increases the drilling demand placed on the point.
Effect of steel strength
Stronger steel can provide greater resistance around the engaged thread, but it can also be more demanding to drill and form. A screw verified in one substrate grade should not automatically be assumed to have the same drilling behaviour or resistance in a substantially different steel grade.
Thickness and strength act together
A thicker low-strength sheet and a thinner high-strength sheet are not automatically equivalent. Connection resistance depends on the interaction between geometry and material properties. Engineering equations and test data normally include both thickness and a relevant steel strength parameter for this reason.
Possible governing modes
- thread pull-out from the supporting steel;
- pull-over or bearing deformation of the attached sheet;
- screw tensile or shear failure;
- combined connection behaviour;
- installation failure before the intended connection is formed.
Drilling capacity is a separate check
A connection may have adequate calculated resistance after installation but still be impractical if the screw cannot reliably drill the specified steel build-up. Structural resistance and drilling capability must therefore be checked separately.
Engineering conclusion
Whenever steel thickness or grade changes, review both installation capability and connection resistance. Do not transfer a capacity value from another substrate condition unless the applicable technical documentation or calculation method explicitly permits it.
This resource explains selection principles. Final product suitability, drilling range and resistance must be verified against the applicable JOPAL technical data for the specific fastener and project condition.
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