12 Step Drill Bit Set, 3 Piece, Spiral Grooved for Faster Drilling, Step Bits for Stainless Steel, Metal, Wood, Plastic, Unibit Cone Drill Bits with 31 Step Sizes Total 12 step drill (3/16, 1/4, 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4, 13/16, 7/8-inch High Speed Steel Versatility Our step drill bits are constructed from traditional HSS combined with a titanium nitride coating to make them even more durable. This also proves the capability and durability of the drill to last through multiple drillings on surfaces such as: plastic, aluminum, copper, stainless steel, and so much more. Unique 2 Flute Spiral Design Two flute spiral design also lets the material particles escape easily for a much more clean drilling operation. With each step, you can feel the drill bit stop so you never drill bigger than you need to.