... )ISO2531,EN545,BS4772 4)Strength,Durability,Safe 1. Ductile iron flexible coupling produced according to ISO2531, EN545, BS4772, EN598, AWWA C110.2 ... StrengthElongationYield StrengthHardnessDuctile iron fittings≥420MPa≥5%≥300MPa≤250HB Ductile iron flexible coupling