M1.6 M2 M2.5 BLACK 10.9/12.9 HIGH TENSILE SOCKET COUNTERSUNK SCREWS BOLTS
Surface: Blackened. There are clear standards in GB/T 3098.1, and the hardness value of bolts can also be found. That is to say, as long as the performance level of the bolt is provided, it is equivalent to defining the strength of the bolt.