The ornamental design for an adaptor for a fasteningtool, as shown and described.
FIG. 1 is a perspective view of an underside of adaptor for a fastening tool;
FIG. 2 is a left-hand side view of the adaptor for a fastening tool of FIG. 1;
FIG. 3 is a bottom view of the adaptor for a fastening tool of FIG. 1;
FIG. 4 is a top view of the adaptor for a fastening tool of FIG. 1;
FIG. 5 is a right-hand perspective view of the adaptor for a fastening tool of FIG. 1;
FIG. 6 is a perspective end view of the adaptor for a fastening tool of FIG. 1; and,
FIG. 7 is a perspective left-hand view as seen from the lower left hand side of the adaptor for a fastening tool of FIG. 1, depicting the adaptor disposed on a fastening tool which is shown in broken line, which is provided only for illustrative purposes, and which forms no part of the claimed design.