Black Iron Square Tube abu ne sanyi birgima carbon karfe madauri tare da bango kauri 0.6mm zuwa 2.0mm.Lokacin da aka yi zafi da madaurin karfe mai sanyi zuwa yanayin zafi, launin saman zai zama baki saboda yawan zafin jiki da iska.Har ila yau mai suna sanyi birgima baki annealed square tube wanda aka yadu amfani ga karfe tsarin.