Trapezoid knives made by Irwin combine the best attributes of two metals and are electro-welded together. The blade edge is made from high-speed steel, which has been shown to last up to 3x longer in user trials on plasterboard, drywall, roofing, insulation, flooring, and other heavy-duty materials. Most of the blade is made of spring steel, which can withstand pressure from the side without snapping. Sharp blades are generally safer to use because they require less effort to cut, and therefore allow for greater control. This blade stays sharp up to 3 x longer than standard blades. The high-speed steel edge, and heat treated to greater hardness for longer life and edge sharpness. Fit all standard knives.