A connecting unit for fixing components in a breathing system includes a plug adapter (2) having a sealing element (1). The sealing element (1) has a first peripheral fastening thickening (4), a second fastening thickening (5) arranged at a distance to the first fastening thickening (4), as well as an undercut (7) between the fastening thickenings (4, 5). The second fastening thickening (5) has an outer lead-in chamfer (6) for a receiving bore into which the plug adapter (2) along with the sealing ring (1) are inserted.
