Twist drills are precision cutting tools, not to be confused with standard "drill bits."Set Contains XL28 Mechanics Length Drill Bits in durable plastic case, water resistant for use in damp environments. XL28 drills; strong rigid overall length. Heavy duty 135 degree split point for self-centering and quick penetration. Heavy duty web geometry provides added rigidity. The three flatted shank design ensures positive grip in keyless drill chucks. Ideal for the aircraft industry. Used for the drilling of high tensile martensitic steels, titanium alloys and hard steel.