Partial thread of small square head bolt

　　Strength: 6.8 Material: carbon steel, alloy steel

　　Material: medium carbon steel

　　Material description: C 0.32-0.39, Mn0.50-0.80，Si0.17-0.37，Cr≤0.25，Cu≤0.25，Ni≤0.30，P≤0.035，S≤0.035， It is similar to American grade 1035, Japanese grade S35C, German, English, and French grade C35, and ISO standard C35E4

　　Surface treatment: Blackening (without quenching)

　　Surface treatment content: Blackening is a common method of metal heat treatment, which is to create a layer of oxide film on the metal surface to isolate air and achieve the purpose of rust prevention.