Different from the square tube, hollow, belongs to the pipe. Steel: A material of various shapes, sizes, and properties required for press forming of steel ingots, billets, or steel. Steel is an indispensable material for the nation's construction and realization of four modernizations. It is widely used and has many varieties. According to the shape of the section, steel is generally divided into four categories: profiles, plates, pipes and metal products. In order to facilitate the production of steel, Order supply and good management, is divided into heavy rail, light rail, large section steel, medium-sized steel, small section steel, steel cold-formed steel, high-quality steel, wire, medium-thick steel, thin steel, electrical silicon steel sheet, strip steel , seamless steel pipe steel, welded steel pipe, metal products and other varieties.

Square steel connector: