I claim the ornamental design for a hand tool adapter, as shown and described.
FIG. 1 is a perspective view of a hand tool adapter showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top end view thereof; and,
FIG. 7 is a bottom end view thereof.
The broken line showing of surface openings shown in the drawings is for the purpose of illustrating portions of the hand tool adapter and forms no part of the claimed design.