PRECISION SCREW DRIVER SET 1.Made of S2 alloy steel,overall heat-treatment 2.Equipped with 31 types of bits,extensive for use PRECISION SCREW DRIVER SET1.Made of S2 alloy steel,overall heat-treatment2.Equipped with 31 types of bits,extensive for use3.Suitable for repairing computer,mobile phone and clock etc. 31PCS PRECISION SCREW DRIVER SET