1/4" Surface Drive x 13mm Standard Universal Made of high quality steel (chrome-molybdenum); thorough and exact heat treatment insures the correct balance of strength and durability Engineered specifically for use with impact tools, using the most up to date industrial specifications Made to transfer the pressure from the thinnest part of the socket wall toward the thicker section, resulting in increased strength Allows up to 20% more torque to be applied than on standard hex impact sockets Lifetime warranty