Abstract: An embodiment of a method for producing a gas treatment device includes disposing a mat support material about a substrate to form a subassembly; passing at least a portion of the subassembly into a main body portion of a housing that has a first portion having a decreasing internal diameter from a first end to the main body portion, the main body portion extending from the first portion.

Abstract: One embodiment of a gas treatment device comprises: a substrate; a housing disposed concentrically about the substrate, the housing comprising a first portion having a decreasing internal diameter from a first end to a main body portion, the main body portion extending from the first portion; and a mat support material disposed concentrically about the substrate to form a subassembly, wherein the subassembly is at least partially disposed in the main body portion.

Abstract: The gas treatment device comprises a shell concentrically disposed around a catalyst substrate comprising a catalyst, and a mat support material disposed between the catalyst substrate and shell, and concentrically around the catalyst substrate. A retainer ring comprising a first wall and a second wall connected by a bridge is concentrically disposed around the catalyst substrate. The retainer ring is in operable communication with the shell to form an interference fit, and also contacts the mat support material. The retainer ring can further comprise at least two segments.