Abstract: In a catalytic converter, a sheet metal housing encloses a pair of sheet metal catalyst pellet beds each having an inner bed member and an outer bed member with the inner bed members having mating peripheral flanges and also forming a plenum between the beds whose air space is maintained by contacting louvers which form the air passage between the beds. A shoulder is formed integral with and extends across each of the outer bed members and is held engaged on its inner bed side with the flange on one of the inner bed members by an extension on the other inner bed member which is sandwiched between the outer bed members while the remaining portions of the mating flanges are received between flanges on the outer bed members.