In the brand of Nippon Steel (JIS series), ordinary structural steel mainly consists of three parts: the first part indicates the material, such as: S (steel) indicates steel, and F (iron) indicates iron;
The second part shows different shapes, types and uses, such as P (plate) for plate, T (tube) for tube and K(Kogu) for tool.
The third part represents the characteristic number, which is generally the lowest tensile strength. For example, SS 400-the first S stands for steel, the second S stands for "structure", and 400 stands for 400MPa with low tensile strength, that is, the general structural steel with an overall tensile strength of 400 MPa.