British Standard Whitworth
Encyclopedia
British Standard Whitworth (BSW) is one of a number of imperial unit
based screw thread
standards which use the same bolt heads and nut hexagonal sizes, the others being British Standard Fine thread
(BSF) and British Standard Cycle
. These three are collectively called Whitworth threads.
The Whitworth thread was the world's first national screw thread standard , 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 0.640327p and a radius of 0.137329p, 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 is 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.
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). Thread pitch is the same in both systems except that the thread pitch for the 0.5 in bolt is 12 threads per inch (tpi) in BSW vs 13 tpi in the UNC.
(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.
(To simplify matters the term hexagon will be used in this paragraph to denote either bolt head or nut). Whitworth spanner (wrench
) markings refer to the bolt diameter rather than the distance across the flats of the hexagon (A/F) as in other standards. Confusion also arises because BSF hexagon sizes can be one size smaller than the corresponding Whitworth hexagon. This leads to instances where a spanner marked 7/16BSF is the same size as one marked 3/8W. In both cases the spanner jaw width of 0.710 in, the width across the hexagon flat, is the same. However, in World War II the size of the Whitworth hexagon was reduced to the same size as the equivalent BSF hexagon purely to save metal during the war, and they never went back to the old sizes afterwards. Thus it is today uncommon to encounter a Whitworth hexagon which takes the nominally correct spanner. Spanners in this case may be marked 7/16BS to indicate that they have a jaw size of 0.710 in and are designed to take either the (later) 7/16 BSW or 7/16 BSF hexagon. The table here http://www.oldengine.org/members/diesel/Tables/WhitAF.htm illustrates the differences between the old and new hexagon standards.
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
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
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).
The Leica Thread-Mount used on rangefinder cameras and on many enlarging lenses is 39 mm by 26 turns-per-inch Whitworth, an artifact of its having been developed by a German company specializing in microscopes and thus equipped with tooling capable of handling threads in inches and in Whitworth.
In the 2011 movie 'Cars 2' by Disney / Pixar, the vital clue to the discovery of the villan, Sir Miles Axlerod, is that he uses Whitworth bolts. The hero, Mater, a tow-truck, knows his stuff! Although Axlerod doesn't precisely resemble any real car (whereas numerous other characters are closely modelled on real cars), he seems most closely to match the orignal Range Rover. In reality, early model Range Rovers used parts with imperial dimensions.
Imperial unit
The system of imperial units or the imperial system is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The system came into official use across the British Empire...
based screw thread
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 a straight thread and the latter called a tapered thread...
standards which use the same bolt heads and nut hexagonal sizes, the others being British Standard Fine thread
British standard fine thread
British standard fine thread is a fine screw thread alternative to British Standard Whitworth thread.It is used for steel bolts and nuts on much British machinery, including automobiles, prior to adoption of the metric standards...
(BSF) and British Standard Cycle
British Standard Cycle
British Standard Cycle or is a British Imperial screw thread standard. Unlike other major British imperial thread standards the thread runs at a 60 degrees rather than a 55 degrees angle...
. 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 , devised and specified by Joseph Whitworth
Joseph Whitworth
Sir Joseph Whitworth, 1st Baronet was an English engineer, entrepreneur, inventor and philanthropist. In 1841, he devised the British Standard Whitworth system, which created an accepted standard for screw threads...
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 0.640327p and a radius of 0.137329p, 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 is 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
SS Xantho
Powered by a horizontal trunk engine, SS Xantho was a steam ship used in the colony of Western Australia as a pearling transport and mothership, as a tramp steamer, carrying passengers, including Aboriginal convicts and trade goods before she sank at Port Gregory, Western Australia in 1872.The...
by the Western Australian Museum
Western Australian Museum
The Western Australian Museum is the state museum for Western Australia.The Western Australian Museum has seven main sites: two in Perth within the Perth Cultural Centre, two in Fremantle , and one each in Albany, Geraldton, and Kalgoorlie-Boulder...
. On disassembly, all its threads were shown to be of the Whitworth type.
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
ISO metric screw thread
The ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.-Basic profile:...
based standards replaced the Imperial ones.
American Unified Coarse
Unified Thread Standard
The Unified Thread Standard defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada...
was originally based on almost the same imperial fractions. The Unified thread angle is 60° and has flattened crests (Whitworth crests are rounded). Thread pitch is the same in both systems except that the thread pitch for the 0.5 in bolt is 12 threads per inch (tpi) in BSW vs 13 tpi in the UNC.
Comparison of standards
The British Standard FineBritish standard fine thread
British standard fine thread is a fine screw thread alternative to British Standard Whitworth thread.It is used for steel bolts and nuts on much British machinery, including automobiles, prior to adoption of the metric standards...
(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
British Standard Cycle
British Standard Cycle or is a British Imperial screw thread standard. Unlike other major British imperial thread standards the thread runs at a 60 degrees rather than a 55 degrees angle...
(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.
(To simplify matters the term hexagon will be used in this paragraph to denote either bolt head or nut). Whitworth spanner (wrench
Wrench
A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning....
) markings refer to the bolt diameter rather than the distance across the flats of the hexagon (A/F) as in other standards. Confusion also arises because BSF hexagon sizes can be one size smaller than the corresponding Whitworth hexagon. This leads to instances where a spanner marked 7/16BSF is the same size as one marked 3/8W. In both cases the spanner jaw width of 0.710 in, the width across the hexagon flat, is the same. However, in World War II the size of the Whitworth hexagon was reduced to the same size as the equivalent BSF hexagon purely to save metal during the war, and they never went back to the old sizes afterwards. Thus it is today uncommon to encounter a Whitworth hexagon which takes the nominally correct spanner. Spanners in this case may be marked 7/16BS to indicate that they have a jaw size of 0.710 in and are designed to take either the (later) 7/16 BSW or 7/16 BSF hexagon. The table here http://www.oldengine.org/members/diesel/Tables/WhitAF.htm illustrates the differences between the old and new hexagon standards.
The British Association screw thread
British Association screw threads
British Association or BA screw threads are a largely obsolete set of small screw threads, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling....
(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 system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...
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 thread
The British Standard Pipe thread is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external with an internal thread.-Types:...
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).
| Whitworth size (in) | Core diameter (in) | Threads per inch | Pitch (in) | Tapping drill size |
|---|---|---|---|---|
| 1/16 | 0.0411 | 60 | 0.0167 | Number Drill 56 (1.2 mm) |
| 3/32 | 0.0672 | 48 | 0.0208 | Number Drill 49 (1.85 mm) |
| 1/8 | 0.0930 | 40 | 0.025 | Number Drill 39 (2.55 mm) |
| 5/32 | 0.1162 | 32 | 0.0313 | Number Drill 30 (3.2 mm) |
| 3/16 | 0.1341 | 24 | 0.0417 | Number Drill 26 (3.7 mm) |
| 7/32 | 0.1654 | 24 | 0.0417 | Number Drill 16 (4.5 mm) |
| 1/4 | 0.1860 | 20 | 0.05 | Number Drill 9 (5.1 mm) |
| 5/16 | 0.2414 | 18 | 0.0556 | Letter Drill F (6.5 mm) |
| 3/8 | 0.2950 | 16 | 0.0625 | 5/16 in (7.94 mm) |
| 7/16 | 0.3460 | 14 | 0.0714 | Letter Drill U (9.3 mm) |
| 1/2 | 0.3933 | 12 | 0.0833 | Letter Drill Z (10.5 mm) |
| 9/16 | 0.4558 | 12 | 0.0833 | 12.1 mm (0.4764 in) |
| 5/8 | 0.5086 | 11 | 0.0909 | 13.5 mm (0.5315 in) |
| 11/16 | 0.5711 | 11 | 0.0909 | 15 mm (0.5906 in) |
| 3/4 | 0.6219 | 10 | 0.1 | 16.27 mm (0.6406 in) |
| 13/16 | 0.6845 | 10 | 0.1 | 18 mm (0.7087 in) |
| 7/8 | 0.7327 | 9 | 0.1111 | 19.25 mm (0.7579 in) |
| 15/16 | 0.7953 | 9 | 0.1111 | 20.75 mm (0.8169 in) |
| 1 | 0.8399 | 8 | 0.125 | 22 mm (0.8661 in) |
| 1 1/8 | 0.9420 | 7 | 0.1429 | |
| 1 1/4 | 1.0670 | 7 | 0.1429 | |
| 1 1/2 | 1.2866 | 6 | 0.1667 | |
| 1 3/4 | 1.4939 | 5 | 0.2 | |
| 2 | 1.7154 | 4.5 | 0.2222 | |
| 2 1/2 | ||||
Current usage
Nearly all current cameras accept a 1/4 in Whitworth tripod thread in their baseplate, while a 5/8 in thread is the accepted standard for tripod mounted land surveying equipment.The Leica Thread-Mount used on rangefinder cameras and on many enlarging lenses is 39 mm by 26 turns-per-inch Whitworth, an artifact of its having been developed by a German company specializing in microscopes and thus equipped with tooling capable of handling threads in inches and in Whitworth.
Historical misuse
British Morris and MG engines from 1919 to 1955 were built in a factory that used metric threads but with bolts and nuts for Whitworth spanners (wrenches) and sockets.In the 2011 movie 'Cars 2' by Disney / Pixar, the vital clue to the discovery of the villan, Sir Miles Axlerod, is that he uses Whitworth bolts. The hero, Mater, a tow-truck, knows his stuff! Although Axlerod doesn't precisely resemble any real car (whereas numerous other characters are closely modelled on real cars), he seems most closely to match the orignal Range Rover. In reality, early model Range Rovers used parts with imperial dimensions.
See also
Other thread standards:- British Association screw threadsBritish Association screw threadsBritish Association or BA screw threads are a largely obsolete set of small screw threads, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling....
(BA) - British standard brass threadBritish standard brass threadBritish standard brass thread is an imperial unit based screw thread. It adopts the Whitworth thread form with a pitch of 26 threads per inch for all diameters...
- British Standard CycleBritish Standard CycleBritish Standard Cycle or is a British Imperial screw thread standard. Unlike other major British imperial thread standards the thread runs at a 60 degrees rather than a 55 degrees angle...
- British standard fine threadBritish standard fine threadBritish standard fine thread is a fine screw thread alternative to British Standard Whitworth thread.It is used for steel bolts and nuts on much British machinery, including automobiles, prior to adoption of the metric standards...
(BSF) - British standard pipe threadBritish standard pipe threadThe British Standard Pipe thread is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external with an internal thread.-Types:...
(BSP) - ISO metric screw threadISO metric screw threadThe ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.-Basic profile:...
- Unified Thread StandardUnified Thread StandardThe Unified Thread Standard defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada...
(UTS, including UNC, UNF, UNS and UNEF)
External links
- Spanner Jaw Sizes Additional information and spanner jaw size table.
- BSW Tapping drill for 65% and 100% and clearance drill sizes.
- http://www.hot.net.au/~kht/ Discusses Whitworth thread and pitch sizes and spanner sizes.
- Conversion chart Whitworth/BSF/AF and metric spanner sizes at foot of page