Bututun ƙarfe yana da sashin rami kuma tsayinsa ya fi girma fiye da diamita ko kewayen ƙarfe. Dangane da siffar sashe, an raba shi zuwa madauwari, murabba'i, rectangular da bututun ƙarfe na musamman; Bisa ga kayan, an raba shi zuwa carbon tsarin karfe bututu, low gami tsarin karfe bututu, gami karfe bututu da hada karfe bututu.