Ф 48 indicates that the outer diameter of the steel pipe (round pipe here) is 48MM；; 2-8 means that the wall thickness is 2 to 8 mm, which is a common expression of steel pipe specifications: outer diameter * wall thickness Ф 48 means that the outer diameter of steel pipe (round pipe here) is 48MM；; 2-8 means that the wall thickness is 2 to 8 mm, which is a common expression of steel pipe specifications: outer diameter * wall thickness Ф 48 means that the outer diameter of steel pipe (round pipe here) is 48MM；; 2-8 means the wall thickness is 2 to 8 mm, which is a common expression of steel pipe specifications: outside diameter * wall thickness.