tubes 20 and 50 will flex accordingly as illustrated in fig7 the arrangement of fig3 whereby the large diameter portion 46 of the outlet tube is spaced from both the inner flexible tube 50 and the overlapped small diameter portion 40 of the inlet tube allows the flexible tubes to bend even though the inner flexible tube 50 is connected to the rigid inlet and outlet tubes thus as shown in fig7 enough space has been provided for the outlet tube 28 to become angled with respect to the inlet tube 26 note that the lengths of the overlapping portions 40 and 46 are sufficient to provide a barrier to the flexible tubes against direct impingement of exhaust gases without this barrier the flexible tubes would not be able to withstand the hostile exhaust gas environment and would ultimately fail during such flexing movement of the coupling the insulation between the flexible tubes will be compressed to a degree at the inside radius of the bend and will be subjected to tension at the outside radius of the bend the preferred insulation being fibrous is quite capable of accommodating this type of movement the arrangement of fig3 is suitable for relatively short couplings which provide enough space for the overlapping inlet and outlet tubes to have sufficient relative angular movement if however the flex requirements of the coupling are severe or the coupling cannot accommodate long overlapping lengths of tubing the arrangement of fig8 is preferred in this modification the basic elements are the same and bear the same reference numerals as in fig3 but an intermediate tube 82 has been added between the inlet and.