The ornamental design for a string trimmer handle, therefor as shown and described.
FIG. 1 is top front perspective view of a string trimmer handle according to the present invention.
FIG. 2 is a top rear perspective view thereof.
FIG. 3 is a bottom front perspective view thereof.
FIG. 4 is a front view thereof.
FIG. 5 is a rear view thereof.
FIG. 6 is a left side view thereof.
FIG. 7 is a right side view thereof.
FIG. 8 is a top view thereof; and,
FIG. 9 is a bottom view thereof.
Any elements shown in broken lines in the Figures form no part of the claimed invention, and are instead included to show environmental aspects of the claimed invention.