Made of superior high speed steel , high hardness and anti ,could be used for quite a long period.Milling , grinding treatment , toughness , hardness , a good helper for breaking taps
Works for removing stripped , rusted , broken , or corroded screws and bolts. Suitable for industrial screw and bolt removal and for everyday home repair work 

M4 / 1#
M5 / 2#
M6 / 3#
M7-8 / 4#
M9-10 / 5#
M11-12 / 6#
M14 / 7#
M16 / 8#
M18-20 / 9#
M22-24 / 10#