Best Way Tools 3 piece rasp drill bit set is made of titanium nitride coated tool steel. This makes the drill bits run cooler, drill smoother and last up to three times longer than your standard drill set. Titanium Nitride (TiN) is an extremely hard ceramic material that protects the steel drill for a longer life (hardness equivalent to 92 HRC). Drill sizes include 1/8", 1/4", and 5/16".