High speed steel with 5 cobalt makes these ideal for drilling extra hard materials split tip enables bits to bite workpiece quickly reducing the need for centre mark drills can be re sharpened without affecting their performance supplied in metal storage case contents 1 15 2 25 3 35 4 45 5 55 6 65 7 75 8 85 9 95 10 105 11 115 12 125 13mm