The ornamental design for a linkingpiece, as shown and described.
FIG. 1 is a perspective view of a first embodiment of a linking piece showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a front elevational view thereof; and,
FIG. 5 is a right side elevational view thereof.
Portions that are shown as broken lines are for illustrative purpose only and form no part of the claimed design. Dot-dash broken lines form boundaries of, but are not included in, the claimed design.