Set of 17 drill bits: 12 titanium nitride-coated high-speed steel drill bits and 5 rotary masonry drill bits. The titanium nitride coating is tough and very smooth, and reduces friction and heat build-up extending the bit's service life to six times more than regular high-speed steel drill bits. Use them for repetitive drilling in most ferrous and nonferrous metals, plastic, and wood. Not recommended for use in aluminum or hard metals such as stainless steel. For a sure grip, all sizes 3/16 in (5 mm) in diameter and larger have three flats on the bit's shank. Their 135 degree split-point tip on all bits 1/8 in (3 mm) in diameter and larger eliminates the need for a center punch and keeps the drill from "walking" on hard surfaces. Masonry drill bits are for rotary drilling in brick, stone, damp and dry masonry, and concrete. Their tough carbide tip and slow spiral flute design ensure efficient material removal, allowing the bit to run cooler and extending service life.