Size --- Drill diameter and recommended screw diameter are engraved on the case. Please note that the thread direction of the screw is standard and the thread direction of the extractor is reverse. Turning the extractor counter-clockwise will tighten it in the hole and engage the broken screw once sufficient grip is achieved.Easy to Use --- Aggressive spiral groove design with left-hand threads (extractor) and right-hand threads (drill) for enhanced grip. When used correctly, opposing rotation helps break loose seized screws. (Note: 3mm screws may be more challenging to extract)Versatile --- Screw extractor bits can also be used for drilling holes in wood, metal, plastic, brick, and masonry.High Quality --- Extractor set made from chrome vanadium steel for high hardness, rust resistance, and long-lasting durability.Convenient --- Ideal for removing damaged, rusted, or stripped screws, bolts, studs, fasteners, pipe plugs, and metal fittings.