The ornamental design for an aftertreatmentdevice for an exhaust treatment system, as shown and described.
FIG. 1 is a left view of the aftertreatment device for an exhaust treatment system;
FIG. 2 is a right view of the aftertreatment device for an exhaust treatment system of FIG. 1;
FIG. 3 is a front view of the aftertreatment device for an exhaust treatment system of FIG. 1;
FIG. 4 is a top view of the aftertreatment device for an exhaust treatment system of FIG. 1; and,
FIG. 5 is a perspective view of the aftertreatment device for an exhaust treatment system of FIG. 1.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.