The ornamental design for a brush handle, as shown.
FIG. 1. is a perspective view of a brush handle showing my new design thereof;
FIG. 2. is a front view thereof;
FIG. 3. is a rear view thereof;
FIG. 4. is a left side view thereof;
FIG. 5. is a right side view thereof;
FIG. 6. is a top plan view thereof; and,
FIG. 7. is an enlarged bottom plan view thereof.
The broken lines illustrate portions of the brush handle that form no part of the claimed design. The eggshell-shaped surfaces on the brush handle, excluding the areas thereon encircled by the broken lines, form a part of the claimed design.