Manufactured from a premium grade of m-7N molybdenum high speed steel. The Nitro Heavy-Duty Construction Reamers have a Ferritic Nitro Carburizing surface treatment which gives a hard protective layer to the reamer. This increases hardness (Rc 75-80) without increasing brittleness which is measurably harder than high speed steel. Body and clearance are gold and black surface treated for maximum lubricity.