The ornamental design for a brush handle, as shown and described.
FIG. 1 is a front perspective view of a brush handle showing our new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing the brush head illustrate environmental subject matter that forms no part of the claimed design. All other broken lines depict portions of the brush handle that form no part of the claimed design.