The hexagon key was first patented in 1909 by William G. Allen (US Patent 960244), but some evidence suggests the idea of a hex turning tool may have been thought of as early as the 1860s. However, due to the difficulty and expense of manufacturing tools with anything but a very basic shape during the 1800s, many were not patented, or patented but not manufactured.
William G. Allen patented a method of cold-forming a female hexagonal recess into screw heads for the Allen Manufacturing Company of Hartford, Connecticut. The company advertised it as the “Allen safety set screw”.
This has led to many referring to them as Allen keys, which is discouraged by the Apex Tool Group, who now own the Allen Manufacturing Company. Widespread use of the name Allen key threatens their ability to keep it as a trademark, though “Allen wrench” was not actually registered as a trademark until 1943.
Howard T. Hallowell Sr, founder of the Standard Pressed Steel Company, wrote in his autobiography about how his company developed a hex key and means of manufacturing it separately from Allen, in 1911. It’s possible this kind of thing happened several times, in more than one country, as its design appears to have been patented by several companies under various names.
These include Inbus in Germany, where it was patented by Bauer und Schaurte, and Brugola in Italy, where it was patented by an Italian manufacturing company owned by Egidio Brugola.
Why was the hexagon key developed?
At the beginning of the 20th century, the most common type of fastener used in industry was a bolt with a square head. The corners of these fastener heads had a tendency to catch on the clothing of workers, leading to frequent accidents.
This created an opportunity for someone to develop a turning tool and a fastener without corners on its head, and reduce the risk of workplace accidents.
Popularisation of the hexagon key
Whilst the hex key was increasingly used in manufacturing industry, it was not until World War II and the resulting huge increase in industrial production that it became commonly used.
Since then, hex fasteners have become common on many products such as cars, bicycles, and furniture. Hex keys will often be included with self-assembly furniture these days as they are cheap to produce.
Further developments of the hexagon key
Since they were first introduced in 1910, subtle developments have been made to the basic hex key design by several companies. These include ball ends, chamfered edges, magnetisation, folding sets, T-handles, spring ring ends, security hex and various surface finishes. For more information on hex key developments see our page What additional features do hexagon keys have?
Why was the Torx design developed?
Torx fasteners and keys were developed by an American tool manufacturing company called Camcar Textron in 1967. The Torx design addressed many of the problems associated with other available fastener designs. Screws with slotted or Philips heads were designed to cam out (see below) in order to prevent fasteners from being overtightened.
What is camming out?
Camming out is when a driver such as a Torx or hex key slips/jumps out of a fastener head that is being driven. This is caused by the torque from the driver (turning tool) exceeding that which the fastener head was designed for.Camming out will often damage the head of the fastener, similar to the way that rounding off can damage a normal bolt head. It can also cause damage to the Torx or hex key, so is something to be avoided wherever possible.
Whilst camming out would prevent damaging the workpiece by over-tightening the fastener, it had several disadvantages. As the driver cams out of the fastener head, it creates wear on both the driver and fastener head. This can make the fastener head look untidy and in severe cases cause the head to round out, making future removal difficult. Wear on the driver reduces its working life, so increases tool costs.
It was also difficult to control the exact torque level that could be applied to a fastener before camming out would occur. With the advent of accurate torque limitation, with tools such as torque wrenches, and the increased use of hex keys and drivers, many of these problems were reduced, but it was still not possible to achieve very high torque loads on a fastener without camming out or stripping the head.
For this reason, the Torx was specifically designed to resist camming out, enabling it to apply far greater torque loads. As they resist camming out, wear is reduced on both the fastener head and driver. It is claimed that this means the life of a Torx bit can be up to ten times that of other fastener drivers.