Our Spiral Grooved Step Drill Bits are made of high quality titanium plated high speed steel, making them extremely durable and resistant to wear. These versatile bits are suitable for use on a variety of materials including wood, metal, and plastic. They feature a 118° X type opening design to prevent slippage, as well as a double spiral flute for efficient chip removal and protection of the cutting edge. These drill bits come in three different sizes: 4mm-12mm, 4mm-20mm, and 4mm-32mm, each with a different blade diameter range and total length. They also have round shank saw drills in three sizes: 3mm, 6mm, and 8mm. All of the drill bits have a shank diameter of 6.35mm/1/4in. In this set, youll receive one of each of the spiral grooved step drill bits, as well as all three saw drills. They come in a convenient plastic box for easy storage and organization. Please note that these drill bits should not be used on stainless steel, and proper safety precautions should always be taken when using any power tool.