FIG. 1 is a top perspective view of a stacking insert;
FIG. 2 is a bottom perspective view of the stacking insert shown in FIG. 1;
FIG. 3 is top plan view thereof;
FIG. 4 is a front elevational view thereof; and,
FIG. 5 is a right-side elevational view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. Broken lines in the FIGS. do not form any part of the claimed design. A left-side elevational view is not shown because it is a mirror image to the right-side elevational view shown in FIG. 5. A rear elevational view is not shown because it is a mirror image to the front elevational view shown in FIG. 4.