IRWIN® Bi-Metal Trapezoid Knife Blades (Pack 100)Irwin Bi Metal Trapezoid Knife Blades combine the best of 2 metals electro welded together. The edge of the blade is made from high speed steel, which is much harder than standard carbon steel, and has been shown to last up to 3x longer in user trials on plasterboard, drywalling, roofing, insulation, flooring and other heavy duty materials. The bulk of the blade is made from spring steel, which can resist pressure applied from the side without