The ornamental design for a hollowstackingcube, as shown and described.
FIG. 1 is a perspective view of a hollow stacking cube showing my new design in use;
FIG. 2 is a top outside view of a first half shell forming the hollow stacking cube, said first half shell seen as the lower shell in FIG. 1;
FIG. 3 is a bottom inside view of the first half shell;
FIG. 4 is a side view of the first half shell, all sides being identical;
FIG. 5 is a top outside view of a second half shell forming the hollow stacking cube, said second half shell seen as the upper shell in FIG. 1;
FIG. 6 is a bottom inside view of the second half shell; and,
FIG. 7 is a side view of the second half shell, all sides being identical.
The hollow stacking cube shown in broken lines in FIG. 1 shows the first and second half shells coupled together to form an assembled unit.
The hollow stacking cube shown in broken lines in FIG. 1 shows the first and second half shells coupled together to form an assembled unit that forms no part of the claimed design.