figures are here incorporated into a fitting 28 they are preferably cold press molded with the latter so as to achieve an unsoldered connection between the inner tube 24 and outer tube 22 on the one hand and a corresponding unsoldered connection between the outer tube 22 and fitting 28 on the other in order to establish a positive and or non positive connection between the outer tube 22 inner tube 24 and fitting 28 the fitting 28 has stepped recesses toward the free end section lying to the left viewed from right to left meaning toward the free end of the tubes 22 24 the end receptacle 12 of the fitting 28 initially has a radially outwardly projecting recess 21 which is bordered by a cylindrical inner wall piece 23 this inner wall section 23 also ends at another radial outwardly directed recess 25 at which is formed a cylindrical section 27 that extends between the free end of the fitting 28 and the radially outwardly directed recess 25 the end receptacle 12 of the fitting 28 is hence successively provided with two stepped shoulders or with corresponding pedestal sections in order to achieve a mutual gas and or fluid tight attachment it is provided that the concentrically telescoping tubes 22 24 be pressed through the.