Wrenches first appeared in the 15th century in the form of a box wrench (see fig. What is a spanner key?). There was no standard size, and each clasp and wrench was made individually by a blacksmith.
It is believed that the first wrenches were used to wind the bowstrings of a crossbow, tightening them so that they were much tighter than the human hand could do.
In the early 16th century, wheel-lock guns were invented that required a box wrench to fire. The wrench loaded the gun by springing the wheel. When the trigger was pulled, the spring was released and the wheel rotated, causing sparks that fired from the pistol.
It was not until the late 18th century that wrenches became diversified in type and use to include all the types we have today. With the onset of the Industrial Revolution, wrought iron wrenches made by blacksmiths were replaced with cast iron versions produced on a larger scale.
By 1825 standard sizes of fasteners and wrenches were developed so that nuts, bolts and wrenches could be interchanged and did not have to be made as a set.
This meant that pieces of equipment could be interchanged, wrenches could be used on multiple fasteners, and nuts could be used on more than one bolt. It also meant that any mechanic could operate the car with their own set of standard wrenches instead of the car always moving with a specific set.
The accuracy of the production of this equipment was quite low, at best accurate to 1/1,000″. By 1841, an engineer named Sir Joseph Whitworth had developed a way to increase the accuracy to 1/10,000 1″ and then, with the invention of the bench micrometer, to 1,000,000/XNUMX″.
With this new technology, the Whitworth standard was developed, which could be replicated in any factory across the country.
During World War II, in order to save materials, the Whitworth standard was adjusted to make fastener heads smaller. This standard became known as the British Standard (BS). Whitworth wrenches can still be used in the new standard, but smaller wrenches must be used instead. For example, a ¼W wrench can be used for 5/16BS fasteners (see illustration). What wrench sizes are available? for more information).
In the 1970s, the UK decided to follow the lead of the rest of Europe and started using the metric system. Wrenches and fasteners began to be produced in completely new sizes, but since equipment made before the 70s is still in use, inch wrenches are sometimes still required.
