1. speed steel construction: These step bits are made of speed steel, offering exceptional strength and durability. Additionally, they feature a titanium nitride coating that reduces friction heat, keeping the bits cooler for extended tool life. 2. Timesaving design: With 29 different opening sizes ranging from 4mm to 32mm, our cone drill bit eliminates the need for frequent bit changes. Save time and effort while effortlessly drilling or enlarging holes of various sizes without interruptions. 3. Smooth bore: The drill bit set ensures fast and smooth drilling on multiple materials, including steel sheets, aluminum sheets, wooden boards, plastic boards, and more. Achieve precise and efficient results every time. 4. Wide applications: Ideal for sheet metal work, sink installation, auto repairs, and more. This stepper drill bit set is designed to cut through various materials such as boards, aluminum, insulation boards, and PVC panels, providing unmatched versatility for your projects.