I claim the ornamental design for a box strap, as shown and described.
FIG. 1 is a perspective view of a box strap, showing my new design in a deployed configuration;
FIG. 2 is a bottom perspective view thereof, illustrated in a flat configuration;
FIG. 3 is a right-side elevational view of FIG. 2, the left-side elevational view being a mirror image thereof;
FIG. 4 is a front elevational view of FIG. 2, the rear elevational view being a mirror image thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The strap is shown broken away in the middle along the length to indicate indeterminate length, with the understanding that the “indeterminate” length portion of the strap not shown forms no part of the claimed design. Patentability is based only on those portions of the article that are shown in solid lines.