The ornamental design for a helicalsleeve of an anchor, as shown and described.
FIG. 1 is a perspective view of a helical sleeve of an anchor according to the design;
FIG. 2 is an additional perspective view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a side view thereof; and,
FIG. 5 is an additional side view thereof.
The dot-dash-dot broken lines and the dot-dot broken line showing of the anchor illustrates the environment of the claimed design and forms no part thereof.