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93-597: The International Auditing and Assurance Standards Board ( IAASB ) is an independent standards body that issues standards, like the International Standards on Auditing , International Standards on Quality Management, and other services, to support the international auditing of financial statements . It is a body supported by the International Foundation for Ethics and Audit. The Public Interest Oversight Board provides oversight of

186-519: A memorandum of understanding to collaborate on the United States Standards Strategy. The determinates of whether an NSB for a particular economy is a public or private sector body may include the historical and traditional roles that the private sector fills in public affairs in that economy or the development stage of that economy. A national standards body (NSB) generally refers to one standardization organization that

279-538: A saw or file , or between coarse grit and fine grit on sandpaper . The common V-thread standards ( ISO 261 and Unified Thread Standard ) include a coarse pitch and a fine pitch for each major diameter. For example, 1 ⁄ 2 -13 belongs to the UNC series (Unified National Coarse) and 1 ⁄ 2 -20 belongs to the UNF series (Unified National Fine). Similarly, M10 (10 mm nominal outer diameter) as per ISO 261 has

372-408: A bit more, yielding thread depths of 60% to 75% of the 0.65 p value. For example, a 75% thread sacrifices only a small amount of strength in exchange for a significant reduction in the force required to cut the thread. The result is that tap and die wear is reduced, the likelihood of breakage is lessened and higher cutting speeds can often be employed. This additional truncation is achieved by using

465-409: A bolt and a nut of the same pitch would fit together: the same requirement must separately be made for the minor and pitch diameters of the threads. Besides providing for a clearance between the crest of the bolt threads and the root of the nut threads, one must also ensure that the clearances are not so excessive as to cause the fasteners to fail. The minor diameter is the lower extreme diameter of

558-422: A coarse thread version at 1.5 mm pitch and a fine thread version at 1.25 mm pitch. The term coarse here does not mean lower quality, nor does the term fine imply higher quality. The terms when used in reference to screw thread pitch have nothing to do with the tolerances used (degree of precision) or the amount of craftsmanship, quality, or cost. They simply refer to the size of the threads relative to

651-407: A company offers a product that is "compliant" with a standard. When an organization develops standards that may be used openly, it is common to have formal rules published regarding the process. This may include: Though it can be a tedious and lengthy process, formal standard setting is essential to developing new technologies. For example, since 1865, the telecommunications industry has depended on

744-479: A cross-sectional view is taken in a plane containing the axis of the threads. For a screw, this is its outside diameter (OD). The major diameter of a nut cannot be directly measured (as it is obstructed by the threads themselves) but it may be tested with go/no-go gauges. The major diameter of external threads is normally smaller than the major diameter of the internal threads, if the threads are designed to fit together. But this requirement alone does not guarantee that

837-453: A direct result of the basic trigonometric functions . It is independent of measurement units (inch vs mm). However, UTS and ISO threads are not sharp threads. The major and minor diameters delimit truncations on either side of the sharp V. The nominal diameter of Metric (e.g. M8) and Unified (e.g. 5 ⁄ 16  in) threads is the theoretical major diameter of the male thread, which is truncated (diametrically) by 0.866 ⁄ 4 of

930-478: A flattened tip (in contrast to Whitworth's 55° angle and rounded tip). The 60° angle was already in common use in America, but Sellers's system promised to make it and all other details of threadform consistent. The Sellers thread, easier to produce, became an important standard in the U.S. during the late 1860s and early 1870s, when it was chosen as a standard for work done under U.S. government contracts, and it

1023-509: A hierarchical fashion in terms of national, regional and international scope; international organizations tend to have as members national organizations; and standards emerging at national level (such as BS 5750 ) can be adopted at regional levels (BS 5750 was adopted as EN 29000) and at international levels (BS 5750 was adopted as ISO 9000). Unless adopted by a government, standards carry no force in law. However, most jurisdictions have truth in advertising laws, and ambiguities can be reduced if

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1116-892: A large variety of independent international standards organizations such as the ASME , ASTM International , the International Commission on Illumination (CIE) , the IEEE , the Internet Engineering Task Force (IETF), SAE International , TAPPI , the World Wide Web Consortium (W3C), and the Universal Postal Union (UPU) develop and publish standards for a variety of international uses. In many such cases, these international standards organizations are not based on

1209-510: A liquid or paste pipe sealant such as pipe dope . The screw thread concept seems to have occurred first to Archimedes , who briefly wrote on spirals as well as designed several simple devices applying the screw principle. Leonardo da Vinci understood the screw principle, and left drawings showing how threads could be cut by machine. In the 1500s, screws appeared in German watches, and were used to fasten suits of armor. In 1569, Besson invented

1302-469: A looser fit than say an H2 tap. Metric uses D or DU limits which is the same system as imperial, but uses D or DU designators for over and undersized respectively, and goes by units of 0.013 mm (0.51 mils). Generally taps come in the range of H1 to H5 and rarely L1. The pitch diameter of a thread is measured where the radial cross section of a single thread equals half the pitch, for example: 16 pitch thread = 1 ⁄ 16   in = 0.0625   in

1395-481: A particular country, while others have been built from scratch by groups of experts who sit on various technical committees (TCs). These three organizations together comprise the World Standards Cooperation (WSC) alliance. ISO is composed of the national standards bodies (NSBs), one per member economy. The IEC is similarly composed of national committees, one per member economy. In some cases,

1488-415: A particular thread, internal or external, is the diameter of a cylindrical surface, axially concentric to the thread, which intersects the thread flanks at equidistant points. When viewed in a cross-sectional plane containing the axis of the thread, the distance between these points being exactly one half the pitch distance. Equivalently, a line running parallel to the axis and a distance D 2 away from it,

1581-471: A perfectly sharp point, and truncation is desirable anyway, because otherwise: In ball screws , the male-female pairs have bearing balls in between. Roller screws use conventional thread forms and threaded rollers instead of balls. The included angle characteristic of the cross-sectional shape is often called the thread angle . For most V-threads, this is standardized as 60 degrees , but any angle can be used. The cross section to measure this angle lies on

1674-611: A permanent agency of the United Nations , in which governments are the primary members, although other organizations (such as non-governmental organizations and individual companies) can also hold a form of direct membership status in the ITU as well. Another example of a treaty-based international standards organization with government membership is the Codex Alimentarius Commission . In addition to these,

1767-414: A plane which includes the axis of the cylinder or cone on which the thread is produced. Lead ( / ˈ l iː d / ) and pitch are closely related concepts. They can be confused because they are the same for most screws. Lead is the distance along the screw's axis that is covered by one complete rotation of the screw thread (360°). Pitch is the distance from the crest of one thread to the next one at

1860-527: A practical commodity. During the next 40 years, standardization continued to occur on the intra- and inter-company levels. No doubt many mechanics of the era participated in this zeitgeist; Joseph Clement was one of those whom history has noted. In 1841, Joseph Whitworth created a design that, through its adoption by many British railway companies, became a standard for the United Kingdom and British Empire called British Standard Whitworth . During

1953-408: A product or process is safe for humans, animals, and the environment. The subject of their work can be narrow or broad. Another area of interest is in defining how the behavior and performance of products is measured and described in data sheets. Overlapping or competing standards bodies tend to cooperate purposefully, by seeking to define boundaries between the scope of their work, and by operating in

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2046-1177: A proposal to form a new global standards body. In October 1946, ISA and UNSCC delegates from 25 countries met in London and agreed to join forces to create the new International Organization for Standardization ; the new organization officially began operations in February ;1947. Standards organizations can be classified by their role, position, and the extent of their influence on the local, national, regional, and global standardization arena. By geographic designation, there are international, regional, and national standards bodies (the latter often referred to as NSBs). By technology or industry designation, there are standards developing organizations (SDOs) and also standards setting organizations (SSOs) also known as consortia. Standards organizations may be governmental, quasi-governmental or non-governmental entities. Quasi- and non-governmental standards organizations are often non-profit organizations. Broadly, an international standards organization develops international standards (this does not necessarily restrict

2139-406: A screw thread depends on its lead , which is the linear distance the screw travels in one revolution. In most applications, the lead of a screw thread is chosen so that friction is sufficient to prevent linear motion being converted to rotary, that is so the screw does not slip even when linear force is applied, as long as no external rotational force is present. This characteristic is essential to

2232-511: A set of threads for watches. In particular applications and certain regions, threads other than the ISO metric screw threads remain commonly used, sometimes because of special application requirements, but mostly for reasons of backward compatibility : The first historically important intra-company standardization of screw threads began with Henry Maudslay around 1800, when the modern screw-cutting lathe made interchangeable V-thread machine screws

2325-449: A similar way that period and frequency are inverses of each other. Coarse threads are those with larger pitch (fewer threads per axial distance), and fine threads are those with smaller pitch (more threads per axial distance). Coarse threads have a larger threadform relative to screw diameter, where fine threads have a smaller threadform relative to screw diameter. This distinction is analogous to that between coarse teeth and fine teeth on

2418-445: A slightly larger tap drill in the case of female threads, or by slightly reducing the diameter of the threaded area of workpiece in the case of male threads, the latter effectively reducing the thread's major diameter . In the case of female threads, tap drill charts typically specify sizes that will produce an approximate 75% thread. A 60% thread may be appropriate in cases where high tensile loading will not be expected. In both cases,

2511-410: A technological baseline for future research and product development. Formal standard setting through standards organizations has numerous benefits for consumers including increased innovation, multiple market participants, reduced production costs, and the efficiency effects of product interchangeability. To support the standard development process, ISO published Good Standardization Practices (GSP) and

2604-496: A university may have copies of technical standards on hand. Major libraries in large cities may also have access to many technical standards. Some users of standards mistakenly assume that all standards are in the public domain . This assumption is correct only for standards produced by the central governments whose publications are not amenable to copyright or to organizations that issue their standard under an open license. Any standards produced by non-governmental entities remain

2697-449: Is a standard used for classifying the tolerance of the thread pitch diameter for taps . For imperial, H or L limits are used which designate how many units of 0.0005 inch over or undersized the pitch diameter is from its basic value, respectively. Thus a tap designated with an H limit of 3, denoted H3 , would have a pitch diameter 0.0005 × 3 = 0.0015 inch larger than base pitch diameter and would thus result in cutting an internal thread with

2790-408: Is known as handedness . Most threads are oriented so that the threaded item, when seen from a point of view on the axis through the center of the helix, moves away from the viewer when it is turned in a clockwise direction, and moves towards the viewer when it is turned counterclockwise. This is known as a right-handed ( RH ) thread, because it follows the right-hand grip rule . Threads oriented in

2883-439: Is less than caliper measurement of the male major diameter (outside diameter, OD). For example, tables of caliper measurements show 0.69 female ID and 0.75 male OD for the standards of "3/4 SAE J512" threads and "3/4-14 UNF JIS SAE-J514 ISO 8434-2". Note the female threads are identified by the corresponding male major diameter (3/4 inch), not by the actual measurement of the female threads. The pitch diameter (PD, or D 2 ) of

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2976-454: Is provided by a class, but the maximum PD of the external thread is specified to be the same as the minimum PD of the internal thread, within specified tolerances, ensuring that the two can be assembled, with some looseness of fit still possible due to the margin of tolerance. A class called interference fit may even provide for negative allowances, where the PD of the screw is greater than the PD of

3069-608: Is that country's member of the ISO . A standards developing organization (SDO) is one of the thousands of industry- or sector-based standards organizations that develop and publish industry specific standards. Some economies feature only an NSB with no other SDOs. Large economies like the United States and Japan have several hundred SDOs, many of which are coordinated by the central NSBs of each country (ANSI and JISC in this case). In some cases, international industry-based SDOs such as

3162-419: Is used as the unit of measurement for pitch, TPI is the reciprocal of pitch and vice versa. For example, a 1 ⁄ 4 -20 thread has 20 TPI, which means that its pitch is 1 ⁄ 20 inch (0.050 in or 1.27 mm). As the distance from the crest of one thread to the next, pitch can be compared to the wavelength of a wave . Another wave analogy is that pitch and TPI are inverses of each other in

3255-864: The African Organisation for Standardisation (ARSO), the Arabic industrial development and mining organization (AIDMO), and others. In the European Union, only standards created by CEN, CENELEC, and ETSI are recognized as European standards (according to Regulation (EU) No 1025/2012 ), and member states are required to notify the European Commission and each other about all the draft technical regulations concerning ICT products and services before they are adopted in national law. These rules were laid down in Directive 98/34/EC with

3348-719: The CIE , the IEEE and the Audio Engineering Society (AES) may have direct liaisons with international standards organizations, having input to international standards without going through a national standards body. SDOs are differentiated from standards setting organizations (SSOs) in that SDOs may be accredited to develop standards using open and transparent processes. Developers of technical standards are generally concerned with interface standards , which detail how products interconnect with each other, and safety standards , which established characteristics ensure that

3441-658: The GCC Standardization Organization (GSO) for Arab States of the Persian Gulf . In general, each country or economy has a single recognized national standards body (NSB). A national standards body is likely the sole member from that economy in ISO; ISO currently has 161 members. National standards bodies usually do not prepare the technical content of standards, which instead is developed by national technical societies. NSBs may be either public or private sector organizations, or combinations of

3534-544: The Hayes command set developed by Hayes , Apple 's TrueType font design and the PCL protocol used by Hewlett-Packard in the computer printers they produced. Normally, the term standards organization is not used to refer to the individual parties participating within the standards developing organization in the capacity of founders, benefactors , stakeholders , members or contributors, who themselves may function as or lead

3627-661: The ISO metric screw threads (M) for most purposes, and BSP threads (R, G) for pipes. These were standardized by the International Organization for Standardization (ISO) in 1947. Although metric threads were mostly unified in 1898 by the International Congress for the standardization of screw threads, separate metric thread standards were used in France, Germany, and Japan, and the Swiss had

3720-516: The ITU to establish the telecommunications standards that have been adopted worldwide. The ITU has created numerous telecommunications standards including telegraph specifications, allocation of telephone numbers, interference protection, and protocols for a variety of communications technologies. The standards that are created through standards organizations lead to improved product quality, ensured interoperability of competitors' products, and they provide

3813-811: The OpenOffice.org , an Apache Software Foundation -sponsored international community of volunteers working on an open-standard software that aims to compete with Microsoft Office , and two commercial groups competing fiercely with each other to develop an industry-wide standard for high-density optical storage . Another example is the Global Food Safety Initiative where members of the Consumer Goods Forum define benchmarking requirements for harmonization and recognize scheme owners using private standards for food safety . Screw thread The mechanical advantage of

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3906-645: The WTO Technical Barriers to Trade (TBT) Committee published the "Six Principles" guiding members in the development of international standards. Some standards – such as the SIF Specification in K12 education – are managed by a non-profit organizations composed of public entities and private entities working in cooperation that then publish the standards under an open license at no charge and requiring no registration. A technical library at

3999-726: The World Health Organization Guidelines in health, or ITU Recommendations in ICT and being publicly funded, are freely available for consideration and use worldwide. In 1904, Crompton represented Britain at the Louisiana Purchase Exposition in St. Louis , Missouri , as part of a delegation by the Institute of Electrical Engineers . He presented a paper on standardization, which

4092-462: The World Wide Web Consortium (W3C), whose standards for HTML , CSS , and XML are used universally. There are also community-driven associations such as the Internet Engineering Task Force (IETF), a worldwide network of volunteers who collaborate to set standards for internet protocols. Some industry-driven standards development efforts don't even have a formal organizational structure. They are projects funded by large corporations. Among them are

4185-406: The intellectual property of their developers (unless specifically designed otherwise) and are protected, just like any other publications , by copyright laws and international treaties . However, the intellectual property extends only to the standard itself and not to its use. For instance if a company sells a device that is compliant with a given standard, it is not liable for further payment to

4278-402: The pitch diameter is not affected. The balancing of truncation versus thread strength is similar to many engineering decisions involving the strength, weight and cost of material, as well as the cost to machine it. Tapered threads are used on fasteners and pipe. A common example of a fastener with a tapered thread is a wood screw . The threaded pipes used in some plumbing installations for

4371-534: The screw-cutting lathe , but the method did not gain traction and screws continued to be made largely by hand for another 150 years. In the 1800s, screw manufacturing began in England during the Industrial Revolution . In these times, there was no such thing as standardization. The bolts made by one manufacturer would not fit the nuts of another. Standardization of screw threads has evolved since

4464-524: The "PD line," slices the sharp-V form of the thread, having flanks coincident with the flanks of the thread under test, at exactly 50% of its height. We have assumed that the flanks have the proper shape, angle, and pitch for the specified thread standard. It is generally unrelated to the major ( D ) and minor ( D 1 ) diameters, especially if the crest and root truncations of the sharp-V form at these diameters are unknown. Everything else being ideal, D 2 , D , & D 1 , together, would fully describe

4557-639: The 1840s through 1860s, this standard was often used in the United States as well, in addition to myriad intra- and inter-company standards. In April 1864, William Sellers presented a paper to the Franklin Institute in Philadelphia , proposing a new standard to replace the US' poorly standardized screw thread practice. Sellers simplified the Whitworth design by adopting a thread profile of 60° and

4650-897: The ARINC Standards. Regional standards bodies also exist, such as the European Committee for Standardization (CEN), the European Committee for Electrotechnical Standardization (CENELEC), the European Telecommunications Standards Institute (ETSI), and the Institute for Reference Materials and Measurements (IRMM) in Europe, the Pacific Area Standards Congress (PASC), the Pan American Standards Commission (COPANT),

4743-461: The IAASB, ensuring that the standards are in the public interest . To further ensure proposed standards are in the public interest the IAASB consults its Consultative Advisory Group, which is composed of standard setters, various international organizations from the private and public sectors, and regulators. Representatives include a balance of users and prepares of financial statements, and should to

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4836-507: The body's first President. The International Federation of the National Standardizing Associations (ISA) was founded in 1926 with a broader remit to enhance international cooperation for all technical standards and specifications. The body was suspended in 1942 during World War II . After the war, ISA was approached by the recently formed United Nations Standards Coordinating Committee (UNSCC) with

4929-515: The contributions of other engineers, accomplished a modest amount of industry standardization; some companies' in-house standards also began to spread more widely within their industries. Joseph Whitworth 's screw thread measurements were adopted as the first (unofficial) national standard by companies around Britain in 1841. It came to be known as the British Standard Whitworth , and was widely adopted in other countries. By

5022-835: The country, and enabled the markets to act more rationally and efficiently, with an increased level of cooperation. After the First World War , similar national bodies were established in other countries. The Deutsches Institut für Normung was set up in Germany in 1917, followed by its counterparts, the American National Standard Institute and the French Commission Permanente de Standardisation , both in 1918. Several international organizations create international standards , such as Codex Alimentarius in food,

5115-409: The crest or root), but instead are truncated, yielding a final thread depth that can be expressed as a fraction of the pitch value. The UTS and ISO standards codify the amount of truncation, including tolerance ranges. A perfectly sharp 60° V-thread will have a depth of thread ("height" from root to crest) equal to 0.866 of the pitch. This fact is intrinsic to the geometry of an equilateral triangle —

5208-404: The cylinder of the screw's body. Each time that the screw's body rotates one turn (360°), it has advanced axially by the width of two ridges. Another way to express this is that lead and pitch are parametrically related, and the parameter that relates them, the number of starts, very often has a value of 1, in which case their relationship becomes equality. In general, lead is equal to pitch times

5301-447: The delivery of fluids under pressure have a threaded section that is slightly conical . Examples are the NPT and BSP series. The seal provided by a threaded pipe joint is created when a tapered externally threaded end is tightened into an end with internal threads. For most pipe joints, a good seal requires the application of a separate sealant into the joint, such as thread seal tape , or

5394-667: The early nineteenth century to facilitate compatibility between different manufacturers and users. The standardization process is still ongoing; in particular there are still (otherwise identical) competing metric and inch-sized thread standards widely used. Standard threads are commonly identified by short letter codes (M, UNC, etc.) which also form the prefix of the standardized designations of individual threads. Additional product standards identify preferred thread sizes for screws and nuts, as well as corresponding bolt head and nut sizes, to facilitate compatibility between spanners (wrenches) and other tools. The most common threads in use are

5487-515: The end of the 19th century differences in standards between companies was making trade increasingly difficult and strained. For instance, in 1895 an iron and steel dealer recorded his displeasure in The Times : "Architects and engineers generally specify such unnecessarily diverse types of sectional material or given work that anything like economical and continuous manufacture becomes impossible. In this country no two professional men are agreed upon

5580-656: The extent practicable be balanced geographically. Founded in March 1978 as the International Auditing Practices Committee (IAPC), the IAASB's current strategic objectives include: Standards body A standards organization , standards body , standards developing organization ( SDO ), or standards setting organization ( SSO ) is an organization whose primary function is developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise contributing to

5673-480: The foreword with a statement like the following: "Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights". If the standards organization is aware that parts of a given standard fall under patent protection, it will often require the patent holder to agree to Reasonable and non-discriminatory licensing before including it in

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5766-577: The galling of the threads. For this reason, some allowance , or minimum difference, between the PDs of the internal and external threads has to generally be provided for, to eliminate the possibility of deviations from the ideal thread form causing interference and to expedite hand assembly up to the length of engagement. Such allowances, or fundamental deviations , as ISO standards call them, are provided for in various degrees in corresponding classes of fit for ranges of thread sizes. At one extreme, no allowance

5859-657: The goal of providing transparency and control with regard to technical regulations. Sub-regional standards organizations also exist such as the MERCOSUR Standardization Association (AMN), the CARICOM Regional Organisation for Standards and Quality (CROSQ), and the ASEAN Consultative Committee for Standards and Quality (ACCSQ), EAC East Africa Standards Committee www.eac-quality.net , and

5952-401: The inability of their developers to keep abreast with the technological innovation. As a result, a new class of standards setters appeared on the standardization arena: the industry consortia or standards setting organizations (SSOs), which are also referred to as private standards . Despite having limited financial resources, some of them enjoy truly international acceptance. One example is

6045-401: The maximum limits for internal ( nut ), thread sizes are there to ensure that threads do not strip at the tensile strength limits for the parent material. The minimum limits for internal, and maximum limits for external, threads are there to ensure that the threads fit together. The major diameter of threads is the larger of two extreme diameters delimiting the height of the thread profile, as

6138-469: The national committee to the IEC of an economy may also be the ISO member from that country or economy. ISO and IEC are private international organizations that are not established by any international treaty. Their members may be non-governmental organizations or governmental agencies, as selected by ISO and IEC (which are privately established organizations). The ITU is a treaty-based organization established as

6231-404: The number of starts. Whereas metric threads are usually defined by their pitch, that is, how much distance per thread, inch-based standards usually use the reverse logic, that is, how many threads occur per a given distance. Thus, inch-based threads are defined in terms of threads per inch (TPI). Pitch and TPI describe the same underlying physical property—merely in different terms. When the inch

6324-619: The nut by at least the amount of the allowance. The pitch diameter of external threads is measured by various methods: The way in which male and female fit together, including play and friction, is classified (categorized) in thread standards. Achieving a certain class of fit requires the ability to work within tolerance ranges for dimension (size) and surface finish . Defining and achieving classes of fit are important for interchangeability . Classes include 1, 2, 3 (loose to tight); A (external) and B (internal); and various systems such as H and D limits. Thread limit or pitch diameter limit

6417-509: The opposing threads, and everything else is ideal, if the pitch diameters of a screw and nut are exactly matched, there should be no play at all between the two as assembled, even in the presence of positive root-crest clearances. This is the case when the flanks of the threads come into intimate contact with one another, before the roots and crests do, if at all. However, this ideal condition would in practice only be approximated and would generally require wrench-assisted assembly, possibly causing

6510-591: The opposite direction are known as left-handed ( LH ). By common convention, right-handedness is the default handedness for screw threads. Therefore, most threaded parts and fasteners have right-handed threads. Left-handed thread applications include: The cross-sectional shape of a thread is often called its form or threadform (also spelled thread form ). It may be square , triangular , trapezoidal , or other shapes. The terms form and threadform sometimes refer to all design aspects taken together (cross-sectional shape, pitch, and diameters), but commonly refer to

6603-437: The pitch actual pitch diameter of the thread is measured at the radial cross section measures 0.03125   in. To achieve a predictably successful mating of male and female threads and assured interchangeability between males and between females, standards for form, size, and finish must exist and be followed. Standardization of threads is discussed below. Screw threads are almost never made perfectly sharp (no truncation at

6696-431: The pitch from the dimension over the tips of the "fundamental" (sharp cornered) triangles. The resulting flats on the crests of the male thread are theoretically one eighth of the pitch wide (expressed with the notation 1 ⁄ 8 p or 0.125 p ), although the actual geometry definition has more variables than that. A full (100%) UTS or ISO thread has a height of around 0.65 p . Threads can be (and often are) truncated

6789-472: The principle of one member per country. Rather, membership in such organizations is open to those interested in joining and willing to agree to the organization's by-laws – having either organizational/corporate or individual technical experts as members. The Airlines Electronic Engineering Committee (AEEC) was formed in 1949 to prepare avionics system engineering standards with other aviation organizations RTCA, EUROCAE, and ICAO. The standards are widely known as

6882-790: The purpose of safety or for consumer protection act from deceitful practices. The term formal standard refers specifically to a specification that has been approved by a standards setting organization. The term de jure standard refers to a standard mandated by legal requirements or refers generally to any formal standard. In contrast, the term de facto standard refers to a specification (or protocol or technology) that has achieved widespread use and acceptance – often without being approved by any standards organization (or receiving such approval only after it already has achieved widespread use). Examples of de facto standards that were not approved by any standards organizations (or at least not approved until after they were in widespread de facto use) include

6975-402: The same point. Because the vast majority of screw threadforms are single-start threadforms, their lead and pitch are the same. Single-start means that there is only one "ridge" wrapped around the cylinder of the screw's body. Each time that the screw's body rotates one turn (360°), it has advanced axially by the width of one ridge. "Double-start" means that there are two "ridges" wrapped around

7068-448: The same with Company C's sphygmomanometer as it does with Company D's, or that all shirts that should not be ironed have the same icon (a clothes iron crossed out with an X) on the label. Most standards are voluntary in the sense that they are offered for adoption by people or industry without being mandated in law. Some standards become mandatory when they are adopted by regulators as legal requirements in particular domains, often for

7161-790: The screw diameter. Coarse threads are more resistant to stripping and cross threading because they have greater flank engagement. Coarse threads install much faster as they require fewer turns per unit length. Finer threads are stronger as they have a larger stress area for the same diameter thread. Fine threads are less likely to vibrate loose as they have a smaller helix angle and allow finer adjustment. Finer threads develop greater preload with less tightening torque. There are three characteristic diameters ( ⌀ ) of threads: major diameter , minor diameter , and pitch diameter : Industry standards specify minimum (min.) and maximum (max.) limits for each of these, for all recognized thread sizes. The minimum limits for external (or bolt , in ISO terminology), and

7254-610: The size and weight of a girder to employ for given work". The Engineering Standards Committee was established in London in 1901 as the world's first national standards body. It subsequently extended its standardization work and became the British Engineering Standards Association in 1918, adopting the name British Standards Institution in 1931 after receiving its Royal Charter in 1929. The national standards were adopted universally throughout

7347-454: The standard. Such an agreement is regarded as a legally binding contract, as in the 2012 case Microsoft v. Motorola . The ever-quickening pace of technology evolution is now more than ever affecting the way new standards are proposed, developed and implemented. Since traditional, widely respected standards organizations tend to operate at a slower pace than technology evolves, many standards they develop are becoming less relevant because of

7440-400: The standardized geometry used by the screw. Major categories of threads include machine threads, material threads, and power threads. Most triangular threadforms are based on an isosceles triangle . These are usually called V-threads or vee-threads because of the shape of the letter V . For 60° V-threads, the isosceles triangle is, more specifically, equilateral . For buttress threads ,

7533-455: The standards organization except in the special case when the organization holds patent rights or some other ownership of the intellectual property described in the standard. It is, however, liable for any patent infringement by its implementation, just as with any other implementation of technology. The standards organizations give no guarantees that patents relevant to a given standard have been identified. ISO standards draw attention to this in

7626-438: The standards organizations. The implementation of standards in industry and commerce became highly important with the onset of the Industrial Revolution and the need for high-precision machine tools and interchangeable parts . Henry Maudslay developed the first industrially practical screw-cutting lathe in 1800, which allowed for the standardization of screw thread sizes for the first time. Maudslay's work, as well as

7719-399: The thread form. Knowledge of PD determines the position of the sharp-V thread form, the sides of which coincide with the straight sides of the thread flanks: e.g., the crest of the external thread would truncate these sides a radial displacement D  −  D 2 away from the position of the PD line. Provided that there are moderate non-negative clearances between the root and crest of

7812-615: The thread. Major diameter minus minor diameter, divided by two, equals the height of the thread. The minor diameter of a nut is its inside diameter. The minor diameter of a bolt can be measured with go/no-go gauges or, directly, with an optical comparator . As shown in the figure at right, threads of equal pitch and angle that have matching minor diameters, with differing major and pitch diameters, may appear to fit snugly, but only do so radially; threads that have only major diameters matching (not shown) could also be visualized as not allowing radial movement. The reduced material condition , due to

7905-416: The threads on an external surface are considered male, while the ones on an internal surface are considered female. For example, a screw has male threads, while its matching hole (whether in nut or substrate) has female threads. This property is called gender . Assembling a male-threaded fastener to a female-threaded one is called mating . The helix of a thread can twist in two possible directions, which

7998-400: The triangle is scalene . The theoretical triangle is usually truncated to varying degrees (that is, the tip of the triangle is cut short). A V-thread in which there is no truncation (or a minuscule amount considered negligible) is called a sharp V-thread . Truncation occurs (and is codified in standards) for practical reasons—the thread-cutting or thread-forming tool cannot practically have

8091-554: The two. For example, the Standards Council of Canada is a Canadian Crown Corporation , Dirección General de Normas is a governmental agency within the Mexican Ministry of Economy, and ANSI is a 501(c)(3) non-profit U.S. organization with members from both the private and public sectors. The National Institute of Standards and Technology (NIST), the U.S. government's standards agency, cooperates with ANSI under

8184-406: The unused spaces between the threads, must be minimized so as not to overly weaken the fasteners. In order to fit a male thread into the corresponding female thread, the female major and minor diameters must be slightly larger than the male major and minor diameters. However this excess does not usually appear in tables of sizes. Calipers measure the female minor diameter (inside diameter, ID), which

8277-1023: The use of other published standards internationally). There are many international standards organizations. The three largest and most well-established such organizations are the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), and the International Telecommunication Union (ITU), which have each existed for more than 50 years (founded in 1947, 1906, and 1865, respectively) and are all based in Geneva , Switzerland . They have established tens of thousands of standards covering almost every conceivable topic. Many of these are then adopted worldwide replacing various incompatible "homegrown" standards. Many of these standards are naturally evolved from those designed in-house within an industry, or by

8370-440: The usefulness of technical standards to those who employ them. Such an organization works to create uniformity across producers, consumers, government agencies, and other relevant parties regarding terminology, product specifications (e.g. size, including units of measure), protocols, and more. Its goals could include ensuring that Company A's external hard drive works on Company B's computer, an individual's blood pressure measures

8463-427: The vast majority of its uses. The tightening of a fastener's screw thread is comparable to driving a wedge into a gap until it sticks fast through friction and slight elastic deformation . Screw threads have several applications: In all of these applications, the screw thread has two main functions: Every matched pair of threads, external and internal , can be described as male and female . Generally speaking,

8556-625: Was also adopted as a standard by highly influential railroad industry corporations such as the Baldwin Locomotive Works and the Pennsylvania Railroad . Other firms adopted it, and it soon became a national standard for the U.S., later becoming generally known as the United States Standard thread (USS thread). Over the next 30 years the standard was further defined and extended and evolved into

8649-406: Was so well received that he was asked to look into the formation of a commission to oversee the process. By 1906, his work was complete and he drew up a permanent terms for the International Electrotechnical Commission . The body held its first meeting that year in London, with representatives from 14 countries. In honour of his contribution to electrical standardization, Lord Kelvin was elected as

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