The ornamental design for a fastener, as shown and described.
FIG. 1 is a perspective view of a fastener depicting an embodiment of a new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a first side view thereof;
FIG. 5 is a second side view thereof; and,
FIG. 6 is a front view thereof.
The broken line portion of the figure drawings is included to show unclaimed subject matter only and forms no part of the claimed design.
All portions of the fastener located between the break lines form no part of the claimed design.
The fastener is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.