. 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.7/16,High Sp Fl 7/16" SH NITRO Construction Reamer Body and clearance are gold and black surface treated for maximum lubricity.