Double-walled fuel supply line element and connecting flange for the same

A connecting flange (124, 125, 144, 145) for a double-walled fuel supply line element (12, 13, 14, 15, 16) configured to be used with a fuel supply system (10) of an internal combustion engine (1) comprises a mounting surface (168, 176, 190) configured to fixedly arrange an outer line element (122, 142) around an inner line element (121, 141) such that a tubular hollow space (123, 143) is provided, an end face (162, 174, 192) opposite to the mounting surface (168, 176, 190) and a central bore (171, 177, 195) extending between the mounting surface and the end face. The end face (162, 174, 192) includes a projection (164) or a recess (178, 191) surrounding the central bore (171, 177, 195), and a pair of circumferentially extending grooves (170) formed in a front surface (166) of the projection (164) or a bottom surface (180) of the recess (178).