pointing second sealing element 40 this end of the plug in piece 1 is adapted for sealing with respect to the outside surface of a tubular shaped hollow body that can be inserted in said end without limitation to generality the first sealing element 30 and the second sealing element 40 lie in the same radial plane in the embodiments shown the advantage of this is that the plug in piece 1 as a connecting element uses no additional installation space since the cylindrical surfaces to be connected that is the tubular shaped hollow bodies can be slipped over each another thus the exemplary embodiments described are suitable in particular for narrow installation spaces in the exemplary embodiments shown in fig7 a b and 8 a b the center point of the sphere lies in approximately the symmetrical axis of the support body 2 analogous to the exemplary embodiments in fig3 and 4 the exemplary embodiment of fig9 is again designed in the shape of a dumb bell with two encircling spherically shaped sealing beads 3 4 and with a wavy fluting at both end faces of the support body 2 it has not only a connecting but also an adapter function since the inside diameter of the support body 2 expands in conical fashion from the one end face to the other end face this plug in piece 1 is adapted for connecting cylindrical surfaces that have different inside diameters the plug in piece 1 shown in fig1 a.