The ornamental design for a base for holding a handle, as shown and described.
FIG. 1 is a front perspective view of a base for holding a 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 the top plan view thereof; and,
FIG. 7 is the bottom plan view thereof.
The broken lines showing the brush handle and the brush head illustrate environmental subject matter that forms no part of the claimed design. All other broken lines depict portions of the base that form no part of the claimed design.