I-beams are mainly divided into ordinary I-beams, lightweight I-beams, and wide flange I-beams. According to the ratio of flange to web height, it is divided into wide, medium, and narrow flange I-beams. The specifications produced by the first two are 10-60, with corresponding heights ranging from 10 cm to 60 cm. At the same height, lightweight I-beams have narrow flanges, thin web plates, and are lightweight. Wide flange I-beam, also known as H-beam, has a cross-sectional characteristic of parallel legs and no slope on the inner side of the legs. It belongs to the economic section steel and is rolled on a four roll rolling mill, so it is also known as "I-beam". Ordinary I-beams and lightweight I-beams have formed national standards. The specifications of I-beams are expressed in centimeters of waist width, such as 10 gauge I-beams, which have a waist width of 10cm. The types of I-beams include hot-rolled ordinary I-beams, lightweight I-beams, and wide parallel leg I-beams (H-beams). The waist width of hot-rolled ordinary I-beams in China ranges from 100 to 630mm, denoted as No.10 to No.63, with a leg inner wall slope of 1:6. The pass systems for rolling I-beams include straight pass system, skew pass system, and hybrid pass system. In addition, I-beams can also be rolled using special rolling methods.