A combustor assembly having a transition piece and at least one orifice assembly in the transition piece, the orifice assembly comprising: a boss having an outside periphery and an inside periphery, the inside periphery including an annular seat and an upstanding flange formed with an annular, inwardly facing retaining ring groove, the boss fixed within an opening in the transition piece; an orifice plate having a bottom surface that is adapted to be received on the annular seat; and a retaining ring located in the retaining ring groove and at least partially engaged with the orifice plate.