Material: Made of high quality hard alloy for long time use. Size: 9mm / 10mm / 11mm / 12mm / 13mm / 14mm / 15mm / 16mm / 17mm / 19mm. This is an 11-piece heavy duty tool set for removing nuts, bolts, screw heads, studs, etc. The teeth cut into spiral provide a positive grip for removing rounded or damaged bolts. Made of hard alloy, they are of high strength and long durability. These tools can be driven with a wrench or a metric socket for quick work.