One or more aftertreatment bricks are axially inserted through an opening in the first end of a tubular sleeve of an aftertreatment system. The aftertreatment brick includes a substrate matrix and a mantle disposed around the substrate matrix. The mantle further includes a lip arranged to extend through the opening of the sleeve. One or more channel pockets are secured proximate to the opening of the sleeve and oriented radially outward with respect to the sleeve axis. To retain the aftertreatment brick in the sleeve, a clamping assembly is used that includes a hook, a fastener, and a capture nut. The capture nut is installed and accommodated in the channel pockets. The hook engages the protruding lip of the aftertreatment brick and the fastener secures the hook to the capture nut received in the channel pocket.