Irwin 10504240 Bi-Metal BLUE Trapezoid Knife Blades (Pack of 5) The Irwin 10504240 is a 5 pack of Bi-Metal BLUE Trapezoid Knife Blades. Bi-Metal is formed by welding highspeed steel edge and spring steel, having the benefit of both types increases safety and a longer life. Irwin Bi-metal BLUE Blades are safer since they will not break under normal working conditions, and they help reduce the risk of injury from breaking or shattering blades. And, with the blades lasting longer than traditional carbon blades, they result in fewer blade changes which means fewer accidental cuts. Features:  SHATTERPROOF - Spring steel allows the blade to bend without accidentally breaking LAST 3 TIMES LONGER - High speed steel hardened cutting edge stays sharp 3 times longer than traditional carbon blades which means more cuts for the money TRAPEZOID BLADES FIT MOST KNIVES - Two-notch blade design fits most utility knives