Hex key

The hex key, also known by the trade name Allen wrench, is essentially a screwdriver with a hexagonal shank and tip. Commonly, a hex key consists of a single length of steel with a hexagonal cross-section, bent to 90º approximately 1/4 down its length to give two arms of unequal length. The arm not inserted into the hexagonal socket of a bolt or screw functions as a handle for turning the key, with both ends being the same diameter. In practice, this enables the tool to be inserted long-arm-in, using the short arm to provide moderate torque; or inserted short-arm-in, using the long arm to provide greater torque.