The ornamental design for a clamp, as shown and described.
FIG. 1 is a perspective view of the clamp of my new design.
FIG. 2. is another perspective view of the clamp of my new design showing it clamped onto a vertical stud used in construction, and a panel of sheet rock positioned horizontally thereon.
FIG. 3 is a front elevational view thereof.
FIG. 4 is a back elevational view thereof.
FIG. 5 is a right side elevational view thereof.
FIG. 6 is a left side elevational view thereof.
FIG. 7 Is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken line elements in FIG. 2, showing a vertical stud to which the clamp is attached, and a sheet rock panel positioned on the clamp, are environmental elements and form no part of my new design.