Irwin Bi-Metal Blue Blades are an ideal choice for replaceable utility blades. The 2084300WK blades are made from a patented bi-metal technology that makes each blade unbreakable under normal conditions and also allows each blade to maintain their sharp edge longer then standard carbon blades. Irwin is setting new standards of performance with the 2084300WK. You can even use the blades with most other standard utility knives.