41Cr4 Steel - Each bolt extractor is made of high hardness 41Cr Chrome Steel for ultra durability and tough strength to avoid damage during high-intensity use. Includes 13pcs Extractors - 1/4", 5/16"(8mm), 3/8", 10mm, 7/16"(11mm), 12mm, 1/2", 13mm, 9/16"(14mm), 5/8"(16mm), 17mm, 11/16", 3/4"(19mm) suitable for use with impact guns, air ratchets, breaker bars, reversible ratchets, spanners. Size Etched on the Surface - Easily identify and select the most suitable size to removal bolt which saves a lot of time, effort, or energy while removing rusted bolts out. Tight Connection - The upgrade twist socket set provides superior connection to increase grip to remove old rusted and stripped bolts. Organized and Easy to Carry - Packed in heavy-duty blow-molded case for easy storage, it's ok to take it to anywhere whether it is in your garage or factory.