Abstract: A flange for connecting two air ducts to one another has a pair of spaced, generally parallel walls and a pair of spaced, generally parallel legs fast with, and extending perpendicular to, the walls. The flange legs are designed to embrace and grip a wall of an air duct while the flange walls define a chamber adapted to receive one leg of an angle serving to connect the flange to a neighboring flange. One of the flange legs is plastically deformed so as to define a cavity and has a surface facing the other flange leg. The cavity is open to this surface and accommodates an elastomeric seal which projects from the cavity to a location beyond the surface. The seal is elastically compressed in the cavity to retain the seal therein and such compression may be achieved by plastically deforming the respective flange leg after the seal has been positioned on the same.