Shrouded tube and coupling therefor

A coupling fabricated from aluminum for attaching an inner fuel carrying tube and an outer containment tube, said coupling having an attaching member having a central passage in axial alignment with the opening in the inner fuel carrying tube, a seating surface at the mating end of said attaching member, a concentric threaded surface axially spaced from said seating surface, a flexible rubber composite sealing element, toroidal in shape frictionally fitted on the outer diameter of said inner fuel carrying tube, a collar on said latter mentioned tube axially restraining said sealing element,

• an inner nut having a concentric threaded surface on its inner diameter and a concentric threaded surface on its outer diameter both of said threaded surfaces being disposed on the end adjacent said concentric threaded surface on said attaching member and said threaded surface on the inner diameter being threadably engageable therewith,
• an outer nut having a concentric threaded surface on its inner diameter threadably engaging said outer threaded surface of said inner nut,
• said inner nut having a depending shoulder engageable with said collar for urging said sealing element in sealing engagement with said seating surface and urging the end of said inner tubes into said central passage, said outer diameter of said inner fuel carrying tube and said inner nut upon coupling said outer nut to bear against said attaching member and a ferrule at the end of said sealing element mounted on the end of said inner fuel carrying tube for preventing the rubber composite material from extruding when said sealing element engages said seating surface.