The ornamental design for a gripportion for a writing instrument, as shown and described.
FIG. 1 is a side elevational view of a grip portion for a writing
instrument showing our new design, the opposite side elevational view
being a mirror image thereof;
FIG. 2 is a front elevational view; and
FIG. 3 is a rear elevational view thereof.
The environmental structure depicted by means of broken lines in FIGS. 1
through 3 is for illustrative purposes only and forms no part of the
claimed design.