Made of high quality steel (chrome-molybdenum)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 Packaged in a metal case Lifetime Warranty The impact deep length fractional socket set features high torque drives. This feature limits the amount of wear on the corners of the fastener and the socket. It also improves the strength of the socket, transfers increased torque to the fastener and allows easier access to tight areas. Each socket is thoroughly made with the correct balance of strength and durability and is tested to the highest specifications to deliver outstanding performance at the most competitive cost. Set contains the following sizes: 3-1/8", 3-1/4", 3-3/8", 3-1/2", 3-5/8", 3-3/4", 3-7/8", 4", 4-1/8", 4-1/4" and 4-1/2".