The ornamental design for a portion of a socket, as shown and described.
FIG. 1 is a perspective view of the portion of a socket showing my new design;
FIG. 2 is a front elevational view thereof (the right side, the left side, the rear elevational views are a mirror image of the front elevational view);
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a cross sectional view, for clarity purpose only, to show the contour of the portion of a socket showing my new design.
The broken lines in the drawings depict environmental subject matter only and form no part of the claimed design.