"Dead As A Doornail" Idiom Definition And Origin

[eppur_se_muova]

1. Ah, I should have known this already.

Clinch nails were used to make wood doors fire-resistant. In the absence of clinching, the heat of a fire can cause boards to warp and pull nails loose, so that flames can penetrate the spaces. With clinching, the door hangs together even when the wood tries to warp, and is considered a "fire door". Clinch nails have to be made of softer iron than common nails to facilitate bending, and are sold as "fire door nails".

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