Size --- The drill bit diameter and recommended break-off screw diameter are engraved on the housing. Please note that the screw thread direction is positive and the splitter thread direction is reversed. Turning the thread disconnector counterclockwise will continuously tighten it in the inner hole and rotate the screw when a certain tightness is achieved. Easy to Use --- Aggressive design with spiral groove for left hand (extractor) and right hand (drill) for extra grip. If the screws turn in opposite directions, the screws will naturally break. (3mm screws can be difficult to work with) Versatile --- Broken screw extractor drills can also be used to drill holes in wood, metal, plastic, bricks and walls. High Quality --- Extractor set for screw removal uses chrome vanadium steel which offers high hardness, rust resistance and durability Practical --- Ideal for removing damaged, rusted or stripped screws, studs, bolts, fixings, fasteners, metal faucets and water pipes, etc.