This standard covers 3-in. through 54-in. ductile-iron pipe centrifugally cast in metal molds or sand-lined molds for water or other liquids with push-on joints and mechanical joints. This standard may be used for pipe with such other types of joints as may be agreed upon at the time of purchase. Major revisions include the following: data for 30-in. and 36-in. pipe in 18-ft laying lengths, originally published as Addendum A21.51a-1968, have been added to this edition; data for 54-in. pipe in 20-ft laying lengths, originally published as Addendum A21.51a-1968, have been added to this edition; and, standard thicknesses for Laying Condition S have been added, this laying condition involves special construction methods that may be used to obtain economy in thickness for water pipe installed under deep cover.