Fernco 4"x3" Flexible Reducing Coupling with 2 Stainless Steel Clamps. It is used to connect cast iron or plastic to cast iron or plastic. This corrosion-resistant, flexible, lead-free, removable, UV-resistant, underground-rated coupling has a maximum working pressure of 4.3 psi and a maximum working temperature of 120 degrees Fahrenheit. It comes with a 1-year warranty against defects in workmanship or materials.