Mayhew Best Way Tools 3pc Rasp Drill Set is made from titanium nitride coated tool steel. This helps the drill bits run cooler, drill smoother and last up to three times longer than your standard drill bit set. Titanium nitride (TiN) is an extremely hard ceramic material that protects the steel bit for extended performance life (hard ness equilavent to 92 HRC). Drill sizes include 1/8", 1/4", and 5/16".