The origin of threaded fasteners is lost in the clouds of time. Records going back to around 250 BC establish that it was Archimedes who explained the mechanical principle of the screw as a form of wedge. He went on to formulate the mathematical characteristics of the helix-a precursor to the invention of the water screw which as its name implied, was developed as a means to move water from rivers for irrigation.
During the 1st century BC, the Greeks and Romans were using the screw principle to press clothes, olives and wine. The Romans were the first to invent hand-cut screws, primarily for wood and these were made either of bronze or silver, but being hand-cut, a major impediment was posed to the popularization of the screw as a fastening concept.
It was Leonardo da Vinci (1452-1519) who came up with the first floating mandrel for screw cutting (as depicted above). This was a major milestone towards the mechanization of production of the screw thread.
Around 1568, engineer to the French court, Jaques Besson, invented the first useable screw cutting lathe. However, hand cutting of screws remained the predominant method for producing screws for another century or so.
The 16th and 17th centuries saw the royal families of Europe vying with each other in showcasing the excellence of their workshops. Many of the inventions of the ornamental turners of the time were later adapted for industrial purposes such as screw cutting. However old methods continued to co-exist with the new. At the same time, the humble metal screw was slowly and surely coming closer to mass production, triggered as it were, by the crying need for interchangeability – a phenomenon which gathered momentum with the advent of the lndustrial Revolution in 1765.
Around this time, modern machining was being conceived in Great Britain and the industrial importance of the lathe for metalwork became indisputable with the invention of the modern lathe in 1797 by Henry Maudsley. His lathe was capable of cutting threads with great precision and therefore, manufacture of threaded fasteners became easier. However, the problem of each manufacturer making them to his own pattern ensured that standardization was still a far cry.
The first serious standardization attempt at thread design came to fruition in 1841, when Maudsley’s brilliant young apprentice Joseph Whitworth (1803-1887) presented his paper on « The Uniform System of Screw Threads » to Great Britain’s lnstitute of Civil Engineers. His system outlined two proposals, namely that the angle of the thread flanks should be standardized at 55 degrees and the number of threads per inch should be standardized for various diameters.
The first serious standardization attempt at thread design came to fruition in 1841, when Maudsley’s brilliant young apprentice Joseph Whitworth (1803-1887) presented his paper on « The Uniform System of Screw Threads » to Great Britain’s lnstitute of Civil Engineers. His system outlined two proposals, namely that the angle of the thread flanks should be standardized at 55 degrees and the number of threads per inch should be standardized for various diameters.Whitworth’s system became the British standard for fasteners still known today as BSW (British Standard Whitworth). For nearly two decades between the 1840s through the 1860s, this standard in addition to many other intra- & inter-company standards was widely used in the USA and Canada as well.
23 years later, in 1864, William Sellers (1824-1905), a highly regarded tool-maker from Philadelphia in the United States, proposed a 60° thread profile with a flattened pyramid top as compared to the Whitworth thread pyramid which was at 55°, with carefully rounded pyramid top. These changes, he claimed would result in his thread needing « just one cutter and lathe » instead of « three kinds of cutters and two kinds of lathe » and so be easier, quicker and more importantly, cheaper to make.
By 1883, practically all of American railroads, which at that time were the largest corporations in the USA, were using the Sellers screw thread suppliers to those railroads to follow suit. So while on the one hand, Britain had adopted the Whitworth system, America chose to go the Sellers way.
These parallel systems did not pose a major problem until World War II as tanks broke down on either side on account of nuts and bolts going loose or wearing out, the replacements that were being rushed in by American factories would not interchange with the original British threads simply because the British and the American thread profiles did not match. Problems such as these associated with lack of interchangeability among American, British and Canadian parts during the war, led to an effort to unify the inch-based standards among these nations which finally bore fruit on November 18, 1949 in Washington D.C., when the Unified Thread Standard (UTS) was brought into effect by the USA, UK and Canada. This was intended to be applied to screw threads used in these countries with the hope that they would be adopted universally.
However, while on the one hand, the USA adopted this standard wholeheartedly, on the other it was not widely taken up in the UK because around the same lime metric thread standards were being adopted in continental Europe where the metric system was overtaking inch based measurement units.
The international Organization for Standardization (ISO) was founded in 1947 with the objective of being able to provide a forum for arriving at consensus between the then existing inch and metric blocs. The metric-based International System of Units (SI) came into being in 1960.
The United Kingdom which was hitherto adopting a wait and watch policy, look the path of continental Europe in aligning with the ISO metric screw thread and so did the rest of the world.
The desire and necessity to reduce costs and improve productivity has been gaining momentum worldwide, leading to a gradual industry bias in favor of metric fastener products. Today, the ISO metric screw thread is firmly entrenched worldwide and in doing so has displaced all former standards, except the UTS.
It’s been a long and winding road for the screw thread from its nondescript beginnings to its present indispensable status as an assembly-agent, with a fastener being available today for every conceivable application.
Along the way, customization has given way to standardization and interchangeability with globalization playing a major wrote in catapulting the humble screw into the modern mass mechanization age.