... 1,Name: Black thread bolt;Thread bolt;Black bolt 2,For the similar bolt,what can we do ?(1), Ability for the material of this ... kind of bolt: Grade3.6,4 ... Grinding and polishing,etc,except mirror finish (3),Ability for the tolerance Roundess0.002mmCylindricity0.003mmRoughnessRa0.32Straightness0.01/200mm 3,How ...