Hex drive ISO 1173 C6.3 (1/4 inch); Drive: Hexagonal Solid 6.3 (1/4 inch) Special steel for extreme use. High precision manufacturing of tips and edges with tight tolerances For electric and pneumatic screwdrivers as well as for manual operation Tough and hard for threaded screws (hard screw joint) Permanent hardness of 59-61 HR C for heavy use in trade and industry. High torque values, far above the DIN standard, over a long service life