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British Standard Whitworth (BSW) is one of a number of imperial-unit-based screw thread standards which use the same hexagonal bolt head and nut sizes, the others being ''British Standard Fine thread'' (BSF) and ''British Standard Cycle''. These three are collectively called Whitworth threads. ==History== :''See also Screw thread > History of standardization'' The Whitworth thread was the world's first national screw thread standard,〔Gilbert, K. R., & Galloway, D. F., 1978, "Machine Tools". In C. Singer, et al., (Eds.), 'A history of technology''. Oxford, Clarendon Press & Lee, S. (Ed.), 1900, ''Dictionary of national biography'', Vol LXI. Smith Elder, London〕 devised and specified by Joseph Whitworth in 1841. Until then, the only standardization was what little had been done by individual people and companies, with some companies' in-house standards spreading a bit within their industries. Whitworth's new standard specified a 55° thread angle and a thread depth of 0.640327''p'' and a radius of 0.137329''p'', where ''p'' is the pitch. The thread pitch increases with diameter in steps specified on a chart. The Whitworth thread system was later to be adopted as a British Standard to become British Standard Whitworth. An example of the use of the Whitworth thread are the Royal Navy's Crimean War gunboats. These are the first instance of "mass-production" techniques being applied to marine engineering as the following quotation from the obituary from ''The Times'' of 24 January 1887 to Sir Joseph Whitworth (1803–1887) shows: An original example of the gunboat type engine was raised from the wreck of the SS ''Xantho'' by the Western Australian Museum. On disassembly, all its threads were shown to be of the Whitworth type.〔McCarthy, M., and Garcia, R., 2004, "Screw Threads on the SS ''Xantho'': A Case of Standardisation in 19th Century Britain". ''The International Journal of Nautical Archaeology'', 33. (1): 54–66.〕 With the adoption of BSW by British railway lines, many of which had previously used their own standard both for threads and for bolt head and nut profiles, and improving manufacturing techniques, it came to dominate British manufacturing. In the USA, BSW was replaced when steel bolts replaced iron, but was still being used for some aluminium parts as late as the 1960s and 1970s when metric based standards replaced the Imperial ones. American Unified Coarse was originally based on almost the same imperial fractions. The Unified thread angle is 60° and has flattened crests (Whitworth crests are rounded). From 1/4 in up to 1 1/2 in, thread pitch is the same in both systems except that the thread pitch for the 1/2 in bolt is 12 threads per inch (tpi) in BSW versus 13 tpi in the UNC. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「British Standard Whitworth」の詳細全文を読む スポンサード リンク
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