All Kennedy screwdriver bits have a hardness of 58 - 62HRC. High alloy chrome molybdenum steel for use on hand and power tools. TX Bit Set T8, 9, 10, 15, 20, 25, 27, 30 and 40. All 1/4” hex. x 25mm overall length, complete with quick release 1/4” hexagon bit adaptor.