The main technical conditions for H - beam cover dimensions, mechanical properties, and chemical composition. Dimensionally, strict tolerances are set for the height, width, web thickness, and flange thickness to ensure compatibility in construction and mechanical assembly. For example, a deviation of ±2mm in height might be allowed for certain sizes. In terms of mechanical properties, tensile strength, yield strength, and elongation are key indicators. Common grades of H - beam, like Q235 and Q355 in China, have specified yield strengths (235MPa and 355MPa respectively) to guarantee load - bearing capacity. Regarding chemical composition, elements such as carbon, manganese, sulfur, and phosphorus are regulated. Excessive sulfur and phosphorus can reduce the ductility and toughness of the H - beam, so their content is usually limited to low levels.