--This is a set of 10 pieces sturdy tools to help remove nuts, bolts, screw heads, studs, etc.. --It fits heads sized 9, 10, 11, 12, 13, 14, 15, 16, 17, and 19mm. --Spiral cut teeth provide a positive grip to remove rounded or damaged bolts. --Made of hard alloy, they are of strong strength and long..