3+1 Size: 1*72mm scale 4-12, 1*72mm scale 4-20, 1*102mm scale 4-32, 1*72mm twist drill bit. The drill bits can handle holes of different sizes.HSS Sturdy and Rustproof: Made of high-quality HSS, it cuts through thin materials quickly. HSS provides extreme durability, and the drill bits are rust resistant. Compatible with electric screwdrivers.Application: Step drill bit suitable for DIY, home, and construction use. Ideal for drilling holes in various materials such as steel, brass, wood, plastic, thin iron plate, aluminum, insulation board, and PVC board. Suitable for ordinary aluminum, iron, and steel plates with thickness up to 4mm and hardness below 25HRC. Not suitable for stainless steel.Twist Drill Bit: Includes a 4mm HSS 6542 twist drill bit for pre-drilling, which helps reduce damage to the step drill bit compared to standard step drill bits. Note: Lubricate stepped bits before each use to maximize lifespan.