The ornamental design for a fastener for suspenders, as shown and described.
FIG. 1 is a front view of a fastener for suspenders showing my new design in a position of use; the broken lines showing a partial human torso representing the environment in which the design resides.
FIG. 2 is a front view of the present design;
FIG. 3 is a right side view of the present design, a corresponding left side view being a mirror image thereof;
FIG. 4 is a rear view of the present design;
FIG. 5 is a bottom view of the present design; and,
FIG. is a top view of the present design.
The broken lines on the surface of the claim depict stitching. All other broken lines in FIG. 1 depict environmental subject matter that forms no part of the claimed design.