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. A shoulder is formed integral with and extends across each of the outer bed members and is engaged on its inner bed side by the flange on one of the inner bed members while the remaining portions of the mating flanges are received between flanges on the outer bed members. The inner bed members thus cooperate with the respective outer bed members to completely separate the pellets in the beds while relative expansion with heat is permitted between the inner bed members and the outer bed members and also between the inner bed members and the housing members.