How did Allen keys get their name?

Allen keys got their name from the Allen Manufacturing Company in Hartford, Connecticut. These tools are also known as Allen hex wrenches, Allen wrenches and Allen L-keys.

William Allen patented a process in 1910 for making hex socket set screws, which did not have the raised square head that other screws of the time had. Allen had to invent another tool, the Allen key, for turning the hex screws. These tools are available both as single units and in sets of different-size keys, called fold-ups, all attached in one tool. The Allen brand, owned today by Apex Tool Group, also manufactures the tool with a T-handle on the end. This style is used when the application of high torque is necessary.