The ornamental design for a multi-grater, as shown and described.
FIG. 1 is an upward looking perspective view of the multi-grater, with the details of the grater disk shown in dashed line format and forming no part of the invention hereof;
FIG. 2 is a right side elevation which is identical to a left side elevation thereof;
FIG. 3 is a front elevation view which is identical to a rear elevation view thereof;
FIG. 4 is a top plan view; and
FIG. 5 is a bottom plan view with the details of the grater disk shown in dashed line format and forming no part of the invention hereof; and,