A dielectric union assembly includes a threaded union body having external threads, a press-fit union body including an annular groove extending inward and an annular projection extending outward that defines an annular channel, an inner O-ring configured to be accommodated in the annular channel of the press-fit union body, a nut including a flange and internal threads configured to threadedly engage the external threads of the threaded union body, an insert configured to dielectrically isolate the threaded union body and the nut from the press-fit union body, a flange ring including an annular recess, a retaining ring configured to fit into the annular recess of the flange ring, and a gasket configured to be compressed between the threaded union body and the press-fit union body. An inner diameter of the flange of the nut is less than or substantially equal to an outer diameter of the annular projection.