The ornamental design for a blockingtool, as shown and described.
FIG. 1 is a side view of an embodiment of a blocking tool.
FIG. 2 is a top view thereof.
FIG. 3 is a bottom view thereof.
FIG. 4 is a first end view thereof; and,
FIG. 5 is a second end view thereof.
The jagged graphics symbols that break the shaft of the blocking tool into two sections in FIGS. 1, 2, and 3 indicate that the appearance of any portion of the article between the break lines forms no part of the claim.