The ornamental design for a portion of a pivot mount, as shown and described.
FIG. 1 is a front perspective view of a portion of a pivot mount showing my new design;
FIG. 2 is a side view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken line immediately adjacent to the shaded area at a top portion of the design represents an unclaimed boundary of the design. The broken line showing of two circular disclaimed regions within the lower shaded area of FIGS. 1 and 2 forms no part of the claimed design. The broken line showing of half ovals in FIG. 5 are for illustrative purposes only and form no part of the claimed design. The broken line showing of through holes and the remainder of the pivot mount is for illustrative purposes only and forms no part of the claimed design.