This is a 10 piece heavy duty tool set for removing nuts, bolts, screw heads, studs etc. It fits 9 head , 10, 11, 12, 13, 14, 15, 16, 17 and 19mm Spiral cut teeth provide a positive grip for removing rounded or damaged bolts En hard alloy, they are of high strength and long durability These tools can be driven with a wrench or metric socket for quick work