Size --- Drill diameter and recommended broken screw diameter are engraved on the case. Please note that the thread direction of the screw is positive and the thread direction of the extractor is reversed. Turning the extractor counter-clockwise will continuously tighten it in the inner hole and rotate the screw when some tightness is achieved. Easy to Use --- Aggressive design with spiral groove for the left hand (puller) and right hand (drill) for extra grip. If the screws rotate 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 features high hardness, rust resistance, and durability Convenient --- Ideal for removing damaged, rusted, or stripped screws, studs, bolts, fasteners, metal faucets, and water pipes.