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British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard, devised and specified by Joseph Whitworth in 1841 and later adopted as a British Standard. It was the world's first national screw thread standard, and is the basis for many other standards, such as BSF , BSP , BSCon , and BSCopper .
The major diameter is given by 6p 1.2, [4]: 12 rounded to two significant figures in mm and the hex head size (across the flats) is 1.75 times the major diameter. BA sizes are specified by the following British Standards: BS 57:1951 — B.A. screws, bolts and nuts
A few sizes are close enough to interchange for most purposes, such as 19 mm (close to 3 ⁄ 4 inch (19.05 mm)), 8 mm (close to 5 ⁄ 16 inch (7.94 mm)) and 4 mm (close to 5 ⁄ 32 inch (3.97 mm)). In reality, a wrench with a width across the flats of exactly 15 mm would fit too tightly to use on a bolt with a width across the flats of 15 mm.
Below is a comprehensive drill and tap size chart for all drills and taps: Inch, imperial, and metric, up to 36.5 millimetres (1.44 in) in diameter. In manufactured parts, holes with female screw threads are often needed; they accept male screws to facilitate the building and fastening of a finished assembly.
Whitworth screw sizes are still used, both for repairing old machinery and where a coarser thread than the metric fastener thread is required. Whitworth became British Standard Whitworth, abbreviated to BSW (BS 84:1956) and the British Standard Fine (BSF) thread was introduced in 1908 because the Whitworth thread was too coarse for some ...
In the modern standard metric version, it is simply a size number, where listed diameter size is the major outer diameter of the external thread. For a taper thread, it is the diameter at the "gauge length" (plus/minus one thread pitch) from the small end of the thread.
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ISO general purpose metric screw threads—Selected sizes for screws, bolts and nuts: V Thread Form ISO 724:1993: ISO general-purpose metric screw threads—Basic dimensions: V Thread Form ISO 725:2009: ISO inch screw threads—Basic dimensions: V Thread Form 51386 DIN 40400: Edison Thread: Round V Thread Form