RIDGID bi-metal hole saws have become more cost-effective while offering maximum cutting performance.They are made with a cutting edge of premium M42 HS steel and have a tooth set design with twice the life of the old hole saws.RIDGID variable tooth pitch hole saws are ideal for wood, plastics, machinable metals, stainless steel alloys and wood with nails. They are now made with a cutting edge of premium M42 HS steel and have a patent-pending tooth set design with twice the life of the old hole saws.