Where the load is transferred
In a screw-to-steel connection, the engaged threads transfer load into the surrounding steel. With thin sheet there is limited engagement depth, so thread geometry and the condition of the formed hole become especially important.
Thickness and thread pitch
Pitch sets the axial spacing between adjacent threads. It affects how the thread interacts with a given sheet thickness, but simply counting the number of visible threads is not a reliable design check. Thread shape, hole size and the mechanical properties of the sheet also influence the connection.
The supporting steel can govern
The screw is normally much harder than the thin steel around it. In pull-out, failure can occur by deformation or shearing of the steel around the engaged thread. A change in sheet strength can therefore change the resistance even when the screw itself is unchanged.
Hole quality matters
For a self-drilling screw, the point creates the hole immediately before the thread enters. For a self-tapping screw, the pilot-hole diameter is set in advance. An oversized hole leaves less material for thread engagement. An undersized hole can increase installation torque and may damage the screw or the formed thread.
Identify the layer that carries the thread
A thin outer sheet may only be clamped while the main thread engagement occurs in a thicker support. In a sheet-to-sheet connection, the resisting thread may be formed entirely in thin material. These two connections have different load paths even if the same screw diameter is used.
Installation can change the result
Overdriving can strip a connection that would otherwise have adequate engagement. Excessive pressure, poor alignment and repeated removal and reinsertion can also damage the formed thread.
What to verify
For a reliable connection, check thread geometry, supporting-steel thickness and strength, hole formation and installation condition. Pull-out values should come from applicable calculations or verified technical data for the relevant material condition.
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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