Bi-metal saws are popular among many users due to the fact it is compatible with a wide variety of materials. The variable pitched teeth allow hole saws to make faster and smoother cuts while also reducing the overall vibrations. The edge of the cutting end of a hole saw is made by fusing two different types of steel together. This manufacturing technique of joining high speed and soft spring steel helps to create a durable product that can cut a wide variety of materials. Due to its strong wear resistance, the high speed steel makes up the outer edge of the saw and forms the cutting edge of the teeth. On the other end of things, the flexible material of the soft spring steel allows the hole saw to absorb damage from drilling holes in difficult materials.