Automatic Transmission Oil Cooler Line Connector by Dorman®. Location: Radiator Side. Finish: Aluminum. Quantity: 1 Piece. Diameter: 3/8″. Thread: 9/16″ x 18. Dorman’s Auto Trans Oil Cooler Line Connectors are constructed from high-quality materials to provide a leak-free connection between transmission lines or between the radiator and the transmission. Replacement restores the radiator to proper operation.