Channel is a cross-section of the groove-shaped strip steel. Its specifications to waist high (h) * leg width (b) * waist thick (d) of millimeters that if the 120 * 53 * 5, said waist high as 120 mm, leg width of 53 mm channel, waist thick 5 mm channel, or 12 # channel. High waist same channel, if several different legs wide and thick waist abc also need to add the model to the right to be different, such as 25a # 25b # 25c # and so on.