Made of top quality materials. Made of special tool steel, with excellent resistance to degradation as a result of intensive and continuous use. Consists of: 3/8 "heads with diameter: 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 24 mm, long heads: 8 mm, 9 mm, 10 mm, 12 mm, 13 mm, 14 mm, 17 mm, 19 mm, spark plug heads: 16 mm and 21 3/8 "extender mm, special prec steel body, makes work easy even in the most difficult working conditions.