The ornamental design for a one piecefastener, as shown and described.
FIG. 1 is a perspective view of a one piece fastener in accordance with my design.
FIG. 2 is a front side view thereof.
FIG. 3 is a right side view thereof.
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
It will be understood that the thread of the one piece fastener uniformly spirals along the length of the shaft.
The one piece 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.