The ornamental design for a coupler for actuator, as shown and described.
FIG. 1 is a top perspective view of a coupler for actuator showing my new design;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof; the left side view is a mirror image of the right side view;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines in the drawings are for the purpose of illustrating unclaimed portions of the coupler for actuator and form no part of the claimed design.