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.
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.
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.
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.
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.
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.
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″.
With this new technology, the Whitworth standard was developed and could be reproduced in any factory across the country.
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).
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.