Fernco 3005-33 3005-33 Proflex 3 in. Neoprene Shielded Coupling

The 3005-33 is a 3 inch Proflex shielded coupling, so it joins 3 inch pipe on both ends. It is a single-size fitting, not an adapter, so both sides need to be 3 inch. For a transition between two different pipe diameters you need a reducing coupling instead.

Yes. A flexible coupling like the 3 inch Proflex 3005-33 exists precisely to join dissimilar 3 inch drain materials, so cast iron to PVC, ABS, clay or copper DWV is the normal application as long as both outside diameters fall in the coupling's 3 inch range. The neoprene sleeve seals against each pipe and the clamps do the holding, so no solvent weld or lead-and-oakum joint is involved.

The Proflex 3005-33 is a shielded coupling: the neoprene sleeve is wrapped in a metal shear band with clamps, rather than being bare rubber with two band clamps only. The shield resists shear and keeps the joint from deflecting under load, which is why shielded couplings are the ones generally accepted in buried and in-wall drainage work. An unshielded flexible coupling is the lighter-duty option for above-ground repair and test-tee style work.

Nothing extra to buy, but you do need the right tool. The 3005-33 ships as a complete assembly (neoprene sleeve, shear shield, clamps), and it is installed by sliding it over the cut pipe ends and tightening the clamps to the manufacturer's torque spec with a torque wrench or torque screwdriver. Hand-tightening with a nut driver is the usual cause of a weeping joint, so plan on having a torque tool on the truck.

The shielded construction is what makes that possible. Because the 3005-33 carries a metal shear shield over the neoprene rather than being a bare rubber sleeve, it is the style of coupling normally permitted underground and in concealed locations, where unshielded couplings are often restricted. Local code still governs, so confirm with your inspector on the specific installation.