Angle joint sheet, also known as angle iron, is a long strip of steel with two sides perpendicular to each other. There are equilateral angle steel and unequal angle steel. The width of both sides of the equilateral angle steel is equal. Its specifications are expressed in millimeters of side width × side width × side thickness. For example, "∟30×30×3" means an equilateral angle steel with a side width of 30 mm and a side thickness of 3 mm. It can also be expressed by model number, which is the number of centimeters of side width, such as ∟3#. The model number does not indicate the dimensions of different side thicknesses in the same model. Therefore, the side width and side thickness dimensions of the angle steel should be filled in completely on the contract and other documents to avoid using the model number alone. The specifications of hot-rolled equilateral angle steel are 2#-20#. Angle steel can be composed of various stress-bearing components according to different needs of the structure, and can also be used as a connector between components. Angel steel is widely used in various building structures and engineering structures, such as roof beams, bridges, transmission towers, lifting and transportation machinery, ships, industrial furnaces, reaction towers, container racks and warehouses.