Electric hardware manufacturers to introduce the use of angle wrench:

When it comes to the origin of inner six angle wrench, we must start from the inner six angle screw with. In some European non English speaking countries, people "Allen key" is called "Unbrako key", the "Unbrako" is actually the earliest in the six corners of the screw brand, by the United States SPS company (Standard Pressed Steel Company) was founded in 1911. SPS previously imported an internal four corner screw from the UK, but the price was very expensive. In order to save costs, SPS decided to make its own production. SPS founder H. T. Hallowell said in his memoir: "we started experimenting with some screws with square holes like the UK, but soon found that this screw wouldn't be accepted in the United states. So we decided to join in the hole on the hexagonal screw." Hallowell's explanation of this history is ambiguous, but according to later generations, SPS has made modifications to avoid the patent dispute of the four corner screws. In short, SPS began to produce this new inner six corner screw, and registered a trademark called "Unbrako", from the "unbreakable" homonym, meaning "unbreakable"". Since then, the six corner screws have gradually replaced the inner four corner screws as a new industry standard. They are widely used in automobile, aircraft, machinery and furniture manufacturing industries.

The origin of "Allen key"

In the six corner screw appeared a wrench with matching. In the "Unbrako", the six corner screw swept the United States in those years, a variety of wrenches were made, but they did not have a unified name.