... ways 4 GB,JIS,ISO,ASTM,BS,DIN the black carbon steel pipe is widely use in conveyor belt transmission,machine rotary ... go there and have a trip. you know the rectangular steel pipe is world wide use in construction,goods shelf,steel sheds ... ,Q195L,Q235 Q460 Q345 and so on Surfacelightly oil , include black, bright and pre-galvanized End cleanThickness toleranceto your standard or ...