All Kennedy screwdriver bits have a hardness of 58 - 62HRC. High alloy chrome molybdenum steel for use on hand and power tools. Contents: 1/2" Sq. drive x 10mm Hex. bit holder TX 10 x 75mm: T20, T25, T30, T40, T45, T50 and T55 TX 10 x 30mm: T20, T25, T30, T40, T45, T50 and T55