An exhaust treatment device comprises: a substrate; an end-cone with a first end disposed about an end of the substrate and a second end comprising a snorkel; a mat support disposed over at least a portion of the end-cone, wherein the mat support comprises a slit in operable communication with a snorkel slot and a keyhole disposed at the opposite end of the slit as the snorkel slot, and wherein at least a portion of the snorkel protrudes through the snorkel slot; and a shell disposed around the mat support.