Black steel hex screw Process:Mahined and turned Surface:BO SGS audited More than 20 years experience in special fastener 1, ... Name:Black steel hex screw;black hex screw;steel hex screw 2,For the similar hex screw,what ... ), Ability for the material of this kind of hex screw: Grade3.6,4.6,4.8,5.6,6.8 ... fastener ,especially the cutting/turning parts. Black steel hex screw