Product Description FERNCO P1060-33 Socket Coupling, 3 From the Manufacturer Fernco Flexible Couplings have found wide acceptance among sewer and plumbing contractors and municipalities because of their quality and ease of installation. Fernco couplings are used for all types of in-house and sewer connections: drain, waste, vent piping, house-to-main, repairs, cut- ins, conductor, roof drains and increasers-reducers.The 3” x 3” Coupling from Fernco have a 4” measurement with fit range of 2.95 x 3.62 inches