At present, there are two types of self tapping screws commonly used in China, namely, cross countersunk head and cross pan head, which belong to the category of national standards. The surface treatment is usually blue zinc plating, which is quenched in production, which is the heat treatment we usually call, so as to strengthen the hardness. However, there are a few businesses that have special requirements and do not need heat treatment. The cost after heat treatment is naturally higher than that without heat treatment, but the hardness is not as high as that after heat treatment, so it depends on what product users use.