The ornamental design for the head of a pair of pliers, as shown and described.
FIG 1 is an elevated perspective view of the head of a pair of pliers showing my new design,
FIG. 2 is a front elevation view thereof shown in a closed position;
FIG. 3 is a rear elevation view thereof.
FIG. 4 is a side elevation view thereof,
FIG. 5 is the opposite side elevation view thereof,
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing portions of the head of a pair of pliers is included for the purpose of illustrating environmental structures and forms no part of the claimed design.