Part of Coupler

FIG. 1 is a bottom, front, right side perspective view of a part of coupler, showing our new design; FIG. 2 is a bottom plan view thereof; FIG. 3 is a top plan view thereof; FIG. 4 is a front view thereof; FIG. 5 is a rear view thereof; FIG. 6 is a left side view thereof; and, FIG. 7 is a right side view thereof. Evenly broken lines depict portions of the part of coupler which form no part of the claimed design. The dot-dash broken line is an invisible boundary line where claimed surfaces of the part of coupler adjoin unclaimed surfaces of the part of coupler; the boundary line itself forms no part of the claimed design.