The ornamental design for a clamp, as shown and described.
FIG. 1 is a perspective view of a clamp showing my new design;
FIG. 2 is a right side elevational view of the clamp of FIG. 1;
FIG. 3 is a left side elevational view of the clamp of FIG. 1;
FIG. 4 is a top plan view of the clamp of FIG. 1;
FIG. 5 is a bottom plan view of the clamp of FIG. 1;
FIG. 6 is a front elevational view of the clamp of FIG. 1; and,
FIG. 7 is a rear elevational view of the clamp of FIG. 1.
The dash dot lines immediately adjacent to the claimed area represent the boundaries of the claimed design. The dashed lines in the figures illustrate the portions of the design that form no part of the claimed design. None of the broken lines form any part of the claimed design.