largely rotationally symmetrical body which comprises a hollow cylindrical screw connecting piece 7 a having an outer thread provided thereupon and a collar 7 b projecting radially from screw connecting piece 7 a a projection for connecting a fluid line which is designed as a hollow cylindrical section 7 c having a bead 7 d is provided on the side of collar 7 b opposite screw connecting piece 7 a a hose for fluid feeding or discharge may be pushed over section 7 c having bead 7 d and secured with the aid of a hose clamp an annular recess 7 e adjoining screw connecting piece 7 a is also provided in collar 7 b on the side of the screw connecting piece for inserting a second o ring seal 9 the two connecting pieces 7 8 may each be designed as metal molded parts for example by deep drawing them from a metal disk a brazing may be provided at least on the side of the collar on the neck piece side in particular in the case of first connecting piece 6 first connecting piece 6 is inserted into a corresponding opening in collector box 4 of heat exchanger 2 and soldered over a wide area with the aid of neck piece 6 a in particular first connecting piece 6 is soldered to form a block in a soldering furnace together with collector boxes 4 formed from brazed sheets and the flat tubes and ribs inserted into passages in the bottom of collector boxes 4 an inner thread into which hollow cylindrical screw connecting piece 7 a of second connecting piece 7 may be screwed by means of its outer thread is provided in.