The ornamental design for a strapfastener, as shown and described.
FIG. 1 is a perspective view of a strap fastener showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is an enlarged view of the detail shown in FIG. 6;
FIG. 9 is an enlarged view of the detail shown in FIG. 7; and,
FIG. 10 is a perspective view of the strap fastener where the strap fastener is in a configuration of use.
The broken lines in the drawings depict a trash can and another strap fastener shown in FIG. 10 represent environment subject matter only and form no part of the claimed design.