This product apply to cutting material: stainless steel thin sheet iron aluminum insulating board PVC board wood etc. Features: its unique structure a bit can open a variety of specifications size of aperture a box on a step drill for drilling. Don't need to use center punch compared with the ordinary twist drill is not easy to break. Site construction a step drill a variety of specifications apply. Deburring chamfering elliptic hole enlargement the function of the twist drill was unable to complete it. Compared with ordinary twist drill smaller shake. Use tool: pistol drill bench drill