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Concept

Whitworth thread

A close-up view of a Whitworth thread, characterized by its rounded crest and root, set against a gradient background.

The first standardised screw thread, proposed by Joseph Whitworth in 1841. It has a thread angle of 55 degrees and a characteristically rounded crest and root, which Whitworth argued reduced stress concentration and machining defects. Adopted across the British Empire and most of the British engineering trade by the late nineteenth century, it survived in specialised forms — British plumbing fittings, vintage motorcycles — long after the Unified and ISO threads displaced it elsewhere.

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