Size --- Drill diameter and recommended screw diameter are engraved on the case. Note that the thread direction of the screw is standard and the thread direction of the extractor is reversed. Turning the extractor counter-clockwise will tighten it in the hole and engage the broken screw for removal.Easy to Use --- Features an aggressive spiral groove design with left-hand puller and right-hand drill for enhanced grip. When used correctly, opposing rotation helps break loose stuck screws. (Note: 3mm screws may be challenging to extract)Versatile --- Screw extractor bits can also be used for drilling holes in wood, metal, plastic, brick, and walls.High Quality --- Made from chrome vanadium steel for high hardness, rust resistance, and long-lasting durability.Convenient --- Ideal for removing damaged, rusted, or stripped screws, studs, bolts, fasteners, metal fixtures, and pipes.