TITANIUM | HIGH SPEED STEEL: Suitable for below 25 hardness of the work piece, such as carbon steel, sheet iron, insulation boards, PVC boards, planks, and wood thickness below 5MM;Quick-change 1/4 hex shank;TWO-FLUTE DESIGN: made the penetration faster without chipping;This compact set replaces 28 individual drill bits;SET INCLUDES: Bit #1 (6 steps): 3/16, 1/4, 5/16, 3/8, 7/16, 1/2; Bit #2 (13 steps): 1/8, 5/32, 3/16, 7/32, 1/4,9/32, 5/16, 11/32, 3/8, 13/32,7/16,15/32,1/2; Bit #3 (9 steps): 1/4, 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4