FIG. 1 is a front elevational view of a left side pillar insert of a pair of car pillar inserts showing my new design; FIG. 2 is a left side elevational view thereof; FIG. 3 is a right side elevational view thereof; FIG. 4 is a rear elevational view thereof; FIG. 5 is a top plan view thereof; FIG. 6 is a bottom plan view thereof; FIG. 7 is a front elevational view of a right side pillar insert of a pair of car pillar inserts; FIG. 8 is a left side elevational view of FIG. 7; FIG. 9 is a right side elevational view of FIG. 7; FIG. 10 is a rear elevational view of FIG. 7; FIG. 11 is a top plan view of FIG. 7; and, FIG. 12 is a bottom plan view of FIG. 7. The car shown as broken lines is for illustrative purposes only and forms no part of the claimed design.