The ornamental design for a stackableunit, as shown and described.
FIG. 1 is a perspective view of a stackable unit;
FIG. 2 is a front view of the stackable unit of FIG. 1;
FIG. 3 is a right-side view of the stackable unit of FIG. 1;
FIG. 4 is a top plan view of the stackable unit of FIG. 1;
FIG. 5 is bottom plan view of the stackable unit of FIG. 1; and,
FIG. 6 is a perspective view of the stackable unit of FIG. 1, the broken lines showing additional racks and bottles for illustrative purposes only.
The rear view of the stackable unit of FIG. 1 is a mirror image of the front view of FIG. 2. The left-side view of the stackable unit of FIG. 1 is a mirror image of the right-side view of FIG. 3.