A combustor apparatus for gas turbine engines, the combustor apparatus defining a combustion zone where air and fuel are burned to create high temperature combustion products, the combustor apparatus comprising: an outer wall defining an interior volume and comprising a fuel inlet opening; coupling structure on the outer wall adjacent to the fuel inlet opening, the coupling structure comprising a threaded inner coupling portion; a fuel injection system at least partially located in the interior volume of the outer wall and comprising fuel supply structure for providing fuel to at least one fuel injector that delivers fuel to be burned in the combustion zone, the fuel supply structure including a threaded inner surface formed from a first material having a first hardness and a first coefficient of thermal expansion; a fuel feed assembly for delivering fuel to the fuel injection system, the fuel feed assembly including a fuel feed pipe that extends through the fuel inlet opening in the outer wall and comprises: an outlet portion formed from the first material and including a threaded outer surface that is threadedly engaged with the threaded inner surface of the fuel supply structure to create a first sealed coupling (SC 1) with the fuel supply structure; and an inlet portion affixed to the outlet portion and formed from a second material having a second hardness softer than the first hardness and a second coefficient of thermal expansion; and a fitting member disposed about and engaged with the inlet portion of the fuel feed pipe and comprising a threaded outer coupling portion, the threaded outer coupling portion being threadedly engaged with the inner coupling portion of the coupling structure to: create a second sealed coupling (SC 2) with the coupling structure; and secure the fuel feed assembly relative to the outer wall. an outer wall defining an interior volume and comprising a fuel inlet opening; coupling structure on the outer wall adjacent to the fuel inlet opening, the coupling structure comprising a threaded inner coupling portion; a fuel injection system at least partially located in the interior volume of the outer wall and comprising fuel supply structure for providing fuel to at least one fuel injector that delivers fuel to be burned in the combustion zone, the fuel supply structure including a threaded inner surface formed from a first material having a first hardness and a first coefficient of thermal expansion; a fuel feed assembly for delivering fuel to the fuel injection system, the fuel feed assembly including a fuel feed pipe that extends through the fuel inlet opening in the outer wall and comprises: an outlet portion formed from the first material and including a threaded outer surface that is threadedly engaged with the threaded inner surface of the fuel supply structure to create a first sealed coupling (SC 1) with the fuel supply structure; and an inlet portion affixed to the outlet portion and formed from a second material having a second hardness softer than the first hardness and a second coefficient of thermal expansion; and an outlet portion formed from the first material and including a threaded outer surface that is threadedly engaged with the threaded inner surface of the fuel supply structure to create a first sealed coupling (SC 1) with the fuel supply structure; and an inlet portion affixed to the outlet portion and formed from a second material having a second hardness softer than the first hardness and a second coefficient of thermal expansion; and a fitting member disposed about and engaged with the inlet portion of the fuel feed pipe and comprising a threaded outer coupling portion, the threaded outer coupling portion being threadedly engaged with the inner coupling portion of the coupling structure to: create a second sealed coupling (SC 2) with the coupling structure; and secure the fuel feed assembly relative to the outer wall. create a second sealed coupling (SC 2) with the coupling structure; and secure the fuel feed assembly relative to the outer wall.