Hex

A hex key (also hex wrench, Allen key, Allen wrench) is a simple driver for bolts or screws that have heads with internal hexagonal recesses (sockets). Hex keys are formed from a single rod of hard hexagonal steel, having blunt ends that fit snugly into similarly shaped screw sockets. The rod is bent to 90°, forming two arms of unequal length resembling an "L" shape. The tool is usually held and twisted by its long arm, creating a relatively large torque at the tip of the short arm; it can also be held by its short arm to access screws in difficult-to-reach locations and to turn screws faster at the expense of torque. Hex keys are designated with a socket size and are manufactured with tight tolerances. As such, they are usually sold in kits that include a variety of sizes. Key length typically increases with size but not necessarily proportionally so. Variants on this design have the short end inserted in a transverse handle, which can contain multiple keys of varying sizes that can be folded into the handle when not in use. While often used generically, the "Allen" name is a registered trademark (circa 1910) of the Allen Manufacturing Company (now Apex Tool Group) of Hartford, Connecticut.