Wrought iron is commercially pure iron, having a very small carbon content (carbon content does not exceed 0.15 per cent), but usually contains some slag. It is tough, malleable, ductile and can be easily welded. Wrought iron pipe, abbreviated as WIP, is used for the water supply in older houses. Wrought iron does not fuse easily so it cannot be cast. Wrought iron is typically threaded into cast iron fittings. Cast iron fittings have tapered threads, not screwed threads. The pipe also comes in black or galvanized.