Coupler

FIG. 1 is a top front left side perspective view of a coupler, of which a top rear right side perspective view is identical, showing a first embodiment of the new design; FIG. 2 is a top plan view thereof; FIG. 3 is a right side view thereof; FIG. 4 is a left side view thereof; FIG. 5 is a front view thereof; FIG. 6 is a rear view thereof; FIG. 7 is a top front left side perspective view of a coupler, of which a top rear right side perspective view is identical, showing a second embodiment of the new design; FIG. 8 is a top plan view thereof; FIG. 9 is a right side view thereof; FIG. 10 is a left side view thereof; FIG. 11 is a front view thereof; and, FIG. 12 is a rear view thereof. Thin evenly broken lines in all the figures depict portions of the coupler which form no part of the claimed design.