2" x 1-1/2" cast iron hub donut, connects 2" service weight cast iron pipe to plain end of 1-1/2" dwv schedule 40 plastic pipe. Fernco donuts are flexible PVC donut-shaped rings for the compression sealing of sewer pipe joints and DWV connections such as sockets, hubs, bells and spigots. They offer all of the properties necessary to create a strong, lasting joint.