A moisture proof, telescoping coupler assembly for electric metal tubes and threaded rigid pipe with an enhanced grounding arrangement both internally and externally for electrically grounding the telescoping tube to the coupler body, Moisture proof sealing is improved by centering the electric metal tube within the coupler body adjacent the seal preventing possible leaking after securing the electric metal tube to one end. A modified arrangement utilizes a snap fitting retaining ring for securing an electric metal tube to the coupler body to provide for unidirectional insertion of an electric metal tube into the open end of a coupler body in a manner that prohibits unintentional separation of the tube and/or retainer ring from the coupler body.