Durable jaws are made of forged high tensile steel with special heat treating, designed for cutting hard material, spring wire guys, hardened chains, high-tensile bolts, etc Max. hardness of material to be cut: Brinell 450/Rockwell C48, 110 Tons/Sq. 162 Kg/square mm Exceeds U.S. Federal specification number GGG-C-740d Type II