The ornamental design for a clamp, as shown and described.
FIG. 1 is a perspective view of a clamp showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a perspective view thereof disposed around a support arm of a satellite dish antenna; and,
FIG. 9 is an enlarged perspective view of the area indicated on FIG. 8.
The broken lines in the drawings form no part of the claimed design. Broken lines formed by equal length dashes show unclaimed subject matter. Dash-dot-dash broken lines shown in the figures are for the purposes of illustrating boundaries which form no part of the claimed design.