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A brief history of the spanner

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Blacksmiths would have made the first nuts, bolts, fasteners and spanners. Spanners first appeared in the 15th century in the form of a box spanner (see What is a box spanner?). There was no standard size and each fastener and spanner would have been made individually by a blacksmith.
Winding a crossbow with a spanner-like tool in the 15th century painting. It is thought that the first spanners were used to wind up crossbow strings, tightening them so they were much more taut than a human hand could produce.
16th century (1500s) wheel-lock pistol box spanner. At the beginning of the 16th century, wheel-lock guns were invented which required a box spanner to fire. The spanner primed the gun by spring-loading a wheel. When the trigger was pressed, the spring was released and the wheel spun, causing sparks which fired the gun.
Industrial revolution in the 18th and 19th century caused spanners to require a standardisation. It wasn’t until the late 18th century that spanners diversified in type and usage to include all the types we have today. With the onset of the industrial revolution, the wrought iron spanners made by blacksmiths were replaced with cast iron versions produced on a larger scale.
Old standardised spanner. Standard sizes for fasteners and spanners were developed by 1825 so that nuts, bolts and spanners could be interchangeable and did not have to be made as a set.
Steam engine mechanic during the industrial revolution using a massive spanner. This meant pieces of machinery could be swapped around, spanners could be used on multiple fasteners and nuts could be used on more than one bolt. It also meant any mechanic could work on a machine with his own set of standardised spanners instead of the machine always travelling with a specific set.
Bench micrometer invented by Sir Joseph Whitworth to measure accurately to one millionth of an inch. The accuracy of the production of this equipment was quite poor, only accurate to within 1/1,000″ at best. By 1841, an engineer named Sir Joseph Whitworth had developed a way of increasing the accuracy to 1/10,000″ and then, with the invention of the bench micrometer, 1/1,000,000″.
Industrial revolution factories could produce standardised fasteners and spanners. With this new technology, the Whitworth standard was developed and could be reproduced in any factory across the country.
Second world war introduced a different standard to reduce the amount of metal used in the fasteners. During World War II, to save materials, the Whitworth standard was adjusted so the heads of the fasteners were smaller. This standard became known as British Standard (BS). Whitworth spanners could still be used on the new standard but a size down would need to be used instead. For example, a ¼W spanner could be used on a 5/16BS fastener (see What spanner sizes are available? for more information).
Metrication was introduced in the 70s to replace imperial spanners and fastener sizes. In the 1970s, Britain decided to follow the rest of Europe and started to use the metric system. Spanners and fasteners began to be made in completely new sizes but, because equipment made before the ’70s is still used, imperial spanners are still required occasionally.