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The Padlock Patent Archive

Three centuries of keeping things shut

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Screw-key lock

Patent drawing of a padlock showing its rounded shackle and body in Figure 1 alongside a tapered screw-key, with internal cross-section views in Figures 2 and 3 revealing a row of sliding threaded tumblers and springs, and Figure 4 showing the lock's interior lever and bolt mechanism with the side plate removed.

IMPROVEMENT IN PADLOCKSWilliam C. McGill · April 1, 1879

United States patent drawings and specifications are works of the U.S. government and are in the public domain — they were never copyrighted. Download them, print them, frame them. Our commentary and descriptions are © 2026 The Padlock Patent Archive.

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