British Standard Whitworth
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British Standard Whitworth (BSW) is a
screw thread A screw 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 a ''straight'' thread and t ...
standard that uses imperial (inch-based) units. It was devised and specified by British engineer
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 screw ...
in 1841, making it the world’s first national screw thread standard. It became widely adopted across the United Kingdom and its former colonies, influencing engineering practices globally. BSW also laid the foundation for several related thread standards, including British Standard Fine (BSF), British Standard Pipe (BSP), British Standard Conduit (BSCon) and British Standard Copper (BSCopper) threads. Although largely superseded by metric standards in modern engineering, BSW remains in use in restoration, vintage machinery, and certain legacy industries.


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 screw ...
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 (BSW). An example of the use of the Whitworth thread are the
Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
's
Crimean War The Crimean War was fought between the Russian Empire and an alliance of the Ottoman Empire, the Second French Empire, the United Kingdom of Great Britain and Ireland, and the Kingdom of Sardinia (1720–1861), Kingdom of Sardinia-Piedmont fro ...
gunboats. These are the first instance of mass-production 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 circ ...
, as the following quotation from the
obituary An obituary (wikt:obit#Etymology 2, obit for short) is an Article (publishing), article about a recently death, deceased person. Newspapers often publish obituaries as Article (publishing), news articles. Although obituaries tend to focus on p ...
from ''
The Times ''The Times'' is a British Newspaper#Daily, daily Newspaper#National, national newspaper based in London. It began in 1785 under the title ''The Daily Universal Register'', adopting its modern name on 1 January 1788. ''The Times'' and its si ...
'' 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 body, statutory authority within the Culture and the Arts Portfolio, established under the ''Museum Act 1969''. The museum has six main sites. The state museum, WA Museum Boola Bardip, is located i ...
. 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 using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
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: Measuring * 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 ...
-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. For example a G½ (half inch) is 20.955 mm 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 (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: Measuring * 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 ...
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 piping, pipes and fittings by mating an external (Gender of connectors and fasteners, male) thread ...
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 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 (fluid dynamics), circulation of a liquid. Examples of liquid cooling technologies include: * Cooling by convection or circulation of coolant, including water cooling * L ...
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 construction set 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 and ...
thread for many years and it is still the thread in use by the French Meccano Company. Fixings for garden gates traditionally used Whitworth
carriage bolt A carriage bolt (also called coach bolt and round-head square-neck bolt) is a type of Bolt (fastener), bolt. It is also known as a cup head bolt in Australia and New Zealand. It is distinguished from other bolts by its shallow Screw#Truss head, ...
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 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, 1st Viscount Nuffield, William Morris's WRM Motors Limited and continue production of the same ve ...
took over the French Hotchkiss engine works which had moved to
Coventry Coventry ( or rarely ) is a City status in the United Kingdom, cathedral city and metropolitan borough in the West Midlands (county), West Midlands county, in England, on the River Sherbourne. Coventry had been a large settlement for centurie ...
during the First World War. The Hotchkiss machine tools were of metric thread but metric spanners were not readily available in Britain at the time, so fasteners were made with metric thread but Whitworth heads.Harvey, Chris (1977) '' (50 m)˜ The Immortal T Series'', Oxford Illustrated Press,


In popular culture

In the 2011 movie ''
Cars 2 ''Cars 2'' is a 2011 American animated spy comedy film produced by Pixar Animation Studios for Walt Disney Pictures. It is the sequel to '' Cars'' (2006), the second film in the ''Cars'' franchise, and the 12th animated film from the studio ...
'' by
Disney The Walt Disney Company, commonly referred to as simply Disney, is an American multinational mass media and entertainment industry, entertainment conglomerate (company), conglomerate headquartered at the Walt Disney Studios (Burbank), Walt Di ...
/
Pixar Pixar (), doing business as Pixar Animation Studios, is an American animation studio based in Emeryville, California, known for its critically and commercially successful computer-animated feature films. Pixar is a subsidiary of Walt Disney ...
, the vital clue to the discovery of the villain, Sir Miles Axlerod, is that he uses Whitworth bolts. Although Axlerod does not precisely resemble any real car (whereas numerous other characters are closely modelled on real cars), he seems most closely to match the original
Range Rover Classic The Range Rover is a Four-wheel drive, 4x4, mid-size off-road vehicle series produced from 1970 to 1996 – initially by the Rover Company, Rover (later Land Rover) division of British Leyland, and latterly by the Rover Group. The first generat ...
. In reality, early model Range Rovers used parts with imperial dimensions, although the photograph of the villain's engine is virtually identical to the later 3.5-litre, single plenum Rover V8 (A design purchased from GM's Buick).


See also

Other thread standards: * British Association screw threads (BA) * British standard brass thread * British Standard Cycle * British standard fine thread (BSF) * British Standard Pipe (BSP) * ISO metric screw thread *
Unified Thread Standard The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wi ...
(UTS, including UNC, UNF, UNS and UNEF)


References


Bibliography

* Oberg, E., Jones, F.D., Hussain, M., McCauley, C.J., Ryffel, H.H. and Heald, R.M. (2008) ''Machinery's handbook : a reference book for the mechanical engineer, designer, manufacturing engineer, draftsman, toolmaker, and machinist'', 28th Ed., New York : Industrial Press, {{ISBN, 978-0-8311-2800-5, p. 1858–1860


External links


Whitworth Threads
Thread standards Screws British Standards