Abstract: The invention relates to a device for butt joining of ducts for carrying gaseous medium, the ducts having a rectangular or square cross section, wherein a profile is fixed along the free end edges of a duct, which profile comprises: an end wall standing perpendicularly on the duct wall; a flange for fixing the duct wall, a hook-shaped member the legs of which extend along the rear side of the end wall of the profile, such that at least the mutually facing front sides of two mutually opposite hook-shaped members of ducts to be connected can be fixed to each other, and wherein a deformable sealing means is arranged on the rear side of the hook-shaped member facing toward the duct wall.