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British Standard Whitworth (BSW) is an imperial-unit-based
screw thread A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called ...
standard, devised and specified by
Joseph Whitworth Sir Joseph Whitworth, 1st Baronet (21 December 1803 – 22 January 1887) was an English engineer, entrepreneur, inventor and philanthropist. In 1841, he devised the British Standard Whitworth system, which created an accepted standard for scre ...
in 1841 and later adopted as a
British Standard British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter and which is formally designated as the national standards body (NSB) for the UK. The BSI Group produces British Standards under the ...
. It was the world's first national screw thread standard, and is the basis for many other standards, such as
BSF BSF may refer to: Organisations * Ballerup-Skovlunde Fodbold, a Danish football club * British Skin Foundation, a UK charity raising money for skin disease and skin cancer research * Bibliothèques Sans Frontières, an international non profit * ...
, BSP, BSCon, and BSCopper.


History

The Whitworth thread was the world's first national screw thread standard, devised and specified by
Joseph Whitworth Sir Joseph Whitworth, 1st Baronet (21 December 1803 – 22 January 1887) was an English engineer, entrepreneur, inventor and philanthropist. In 1841, he devised the British Standard Whitworth system, which created an accepted standard for scre ...
in 1841. Until then, the only standardization was what little had been done by individual people and companies, with some companies'
in-house Outsourcing is an agreement in which one company hires another company to be responsible for a planned or existing activity which otherwise is or could be carried out internally, i.e. in-house, and sometimes involves transferring employees and ...
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 (BSW). An example of the use of the Whitworth thread are the
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by Kingdom of England, English and Kingdom of Scotland, Scottish kings from the early medieval period, the first major maritime engagements were foug ...
's
Crimean War The Crimean War, , was fought from October 1853 to February 1856 between Russia and an ultimately victorious alliance of the Ottoman Empire, France, the United Kingdom and Piedmont-Sardinia. Geopolitical causes of the war included t ...
gunboats. These are the first instance of
mass-production Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and batch ...
techniques being applied to
marine engineering Marine engineering is the engineering of boats, ships, submarines, and any other marine vessel. Here it is also taken to include the engineering of other ocean systems and structures – referred to in certain academic and professional circl ...
, as the following quotation from the obituary from ''
The Times ''The Times'' is a British daily national newspaper based in London. It began in 1785 under the title ''The Daily Universal Register'', adopting its current name on 1 January 1788. ''The Times'' and its sister paper '' The Sunday Times'' ...
'' of 24 January 1887 for 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 The Western Australian Museum is a statutory authority within the Culture and the Arts Portfolio, established under the ''Museum Act 1969''. The museum has six main sites. The state museum, now known as WA Museum Boola Bardip, officially re-op ...
. On disassembly, all its threads were shown to be of the Whitworth type. With the adoption of BSW by British
railway Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in Track (rail transport), tracks. In contrast to road transport, where the ...
companies, many of which had previously used their own standards both for threads and for bolt head and nut profiles, and the growing need generally for standardisation in manufacturing specifications, it came to dominate British manufacturing. In the US, 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 Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathem ...
-based standards International Inch replaced the U.S. inch and U.K. inch in 1951-1964. American Unified Coarse (UNC) was originally based on almost the same Imperial fractions. The Unified thread angle is 60° and has flattened crests (Whitworth crests are rounded). From  in up to  in, thread pitch is the same in both systems except that the thread pitch for the  in bolt is 12 threads per inch (tpi) in BSW versus 13 tpi in the UNC.


Thread form

The form of a Whitworth thread is based on a fundamental triangle with an angle of 55° at each peak and valley. The sides are at a flank angle of ''Θ'' = 27.5° perpendicular to the axis. Thus, if the thread pitch is ''p'', the height of the fundamental triangle is ''H'' = ''p''/(2tan''Θ'') = 0.96049106''p''. However, the top and bottom of each of these triangles is cut off, so the actual depth of thread (the difference between major and minor diameters) is of that value, or ''h'' = ''p''/(3tan''Θ'') = 0.64032738''p''. The peaks are further reduced by rounding them with a 2×(90° − ''Θ'') = 180° − 55° = 125° circular arc. This arc has a height of ''e'' = ''H''sin ''Θ''/6 = 0.073917569''p'' (leaving a straight flank depth of ''h'' − 2''e'' = 0.49249224''p'') and a radius of ''r'' = ''e''/(1 − sin ''Θ'') = 0.13732908''p''.


List of thread sizes

Below is the historical thread size table, not to be confused with G threads, which are actually in use as
British Standard Pipe British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread. It has b ...
. For example a G½ (half inch) is 20.955mm in diameter.Pipe Thread size Cha

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Spanner (Wrench) size

To simplify matters, the term hexagon is used in this section to denote either bolt head or nut. Whitworth and BSF wrench, spanner markings refer to the bolt diameter, rather than the distance across the flats of the hexagon (A/F) as in other standards. Confusion can arise because each Whitworth hexagon was originally one size larger than that of the corresponding BSF fastener. This leads to instances where for example, a spanner marked '' BSF'' is the same size as one marked '' W''. In both cases the spanner jaw width of 0.710 in, the width across the hexagon flat, is the same. Certain branches of industry used Whitworth fasteners with a smaller hexagon (identical to BSF of the same bolt diameter) under the designation "AutoWhit" or Auto-Whit and this series was formalised by the British Engineering Standards Association in 1929 as standard No. 193, with the 'original' series being No. 190 and the BSF series No. 191. During World War II the smaller size hexagon was adopted more widely to save metal and this usage persisted thereafter. Thus it is today common to encounter a Whitworth hexagon which does not fit the nominally correct spanner and following the previous example, a more modern spanner may be marked '' BS'' to indicate that they have a jaw size of 0.710 in and designed to take either the (later) '' BSW'' or '' BSF'' hexagon. Whitworth fasteners with the larger hexagons to BS 190 are now often colloquially referred to as 'pre-war' size, even though that is not strictly correct.


List of hex head sizes


Comparison with other standards

The
British Standard Fine British Standard Fine (BSF) is a screw thread form, as a fine-pitch alternative to British Standard Whitworth (BSW) thread. It was used for steel bolts and nuts on and in much of Britain's machinery, including cars, prior to adoption of Unified, an ...
(BSF) standard has the same thread angle as the BSW, but has a finer thread pitch and smaller thread depth. This is more like the modern "mechanical" screw and was used for fine machinery and for steel bolts. The British Standard Cycle (BSC) standard which replaced the Cycle Engineers' Institute (CEI) standard was used on British bicycles and motorcycles. It uses a thread angle of 60° compared to the Whitworth 55° and very fine thread pitches. The British Association screw thread (BA) standard is sometimes classed with the Whitworth standard fasteners because it is often found in the same machinery as the Whitworth standard. However it is actually a
metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathem ...
based standard that uses a 47.5° thread angle and has its own set of head sizes. BA threads have diameters of 6 mm (''0BA'') and smaller, and were and still are particularly used in precision machinery. The Whitworth 55° angle remains commonly used today worldwide in form of the 15
British standard pipe thread British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread. It has ...
s defined in ISO 7, which are commonly used in water supply, cooling, pneumatics, and hydraulic systems. These threads are designated by a number between 1/16 and 6 that originates from the nominal internal diameter (i/d) in inches of a steel pipe for which these threads were designed. These pipe thread designations do not refer to any thread diameter. Other threads that used the Whitworth 55° angle include Brass Threads, British Standard Conduit (BSCon), Model Engineers' (ME), and British Standard Copper (BSCopper).


Current usage

The widely used (except in the US)
British Standard Pipe British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread. It has b ...
thread, as defined by the ISO 228 standard (formerly BS-2779), uses Whitworth standard thread form. Even in the United States, personal computer
liquid cooling Liquid cooling refers to cooling by means of the convection or circulation of a liquid. Examples of liquid cooling technologies include: * Cooling by convection or circulation of coolant, including water cooling * Liquid cooling and ventilat ...
components use the G thread from this series. The Leica Thread-Mount used on rangefinder cameras and on many enlarging lenses is  in by 26 turns-per-inch Whitworth, an artifact of this having been developed by a German company specializing in microscopes and thus equipped with tooling capable of handling threads in inches and in Whitworth. The  in Whitworth threads have been the standard
Meccano Meccano is a brand of model construction system created in 1898 by Frank Hornby in Liverpool, England. The system consists of reusable metal strips, plates, angle girders, wheels, axles and gears, and plastic parts that are connected using nuts ...
thread for many years and it is still the thread in use by the French Meccano Company.
Stage lighting Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts.
suspension bolts are most commonly  in and  in BSW. Companies that initially converted to metric threads have converted back, after complaints that the finer metric threads increased the time and difficulty of setup, which often takes place at the top of a ladder or scaffold. Fixings for garden gates traditionally used Whitworth
carriage bolt A carriage bolt (also called coach bolt and round-head square-neck bolt) is a form of bolt used to fasten metal to metal or, more commonly, wood to metal. Also known as a cup head bolt in Australia and New Zealand. It is distinguished from other ...
s, and these are still the standard supplied in UK and Australia.


Historical misuse

British Morris and MG engines from 1923 to 1955 were built using metric threads but with bolt heads and nuts dimensioned for Whitworth spanners and sockets. In 1919,
Morris Motors Morris Motors Limited was a British privately owned motor vehicle manufacturing company formed in 1919 to take over the assets of William Morris's WRM Motors Limited and continue production of the same vehicles. By 1926 its production represen ...
took over the French
Hotchkiss Hotchkiss may refer to: Places Canada * Hotchkiss, Alberta * Hotchkiss, Calgary United States * Hotchkiss, Colorado * Hotchkiss, Virginia * Hotchkiss, West Virginia Business and industry * Hotchki