* A hex key, Allen key or Allen wrench is a tool of hexagonal cross-section used to drive bolts and screws that have a hexagonal socket in the head (internal-wrenching hexagon drive). * The Allen name is a registered trademark, originated by the Allen Manufacturing Company of Hartford, Connecticut circa 1910, and currently owned by Apex Tool Group, LLC * Its genericised use is discouraged by this company. The standard generic name used in catalogues and published books and journals is " hex key" * The contact surfaces of the screw or bolt are protected from external damage and the Torque is constrained by the length and thickness of the key *