The ornamental design for a cam for camlock, as shown and described.
FIG. 1 is a perspective view of a cam for cam lock showing my new design;
FIG. 2 is a top view;
FIG. 3 is a left side view, the right side being symmetrical;
FIG. 4 is a bottom view;
FIG. 5 is an illustrative view of the cam mounted on a cam lock. The broken lines showing of a cam lock is for illustrative purposes only and forms no part of the claimed design;
FIG. 6 is an additional perspective view from the front and bottom; and,
FIG. 7 is an additional perspective view from the rear and bottom.