Cross recessed round head screws are generally made of iron and stainless steel. Iron in the market price is much cheaper than stainless steel. Iron cross-slot round head screws are generally A3 steel materials to manufacture. A3 steel is low, medium and high carbon steel. Stainless steel refers to a lot, there are stainless steel SUS201, SUS304, SUS316 and so on. And iron cross-slot round head screws some hardness and strength requirements of a little higher, you need to add hard heat treatment. Place the round head screws on the fire. Deepen its strength and hardness levels. So that it reaches a certain intensity.