The ornamental design for a boltanchor for concrete, as shown and described.
FIG. 1 is a perspective view of the bolt anchor for concrete according to the invention, with normally exposed end of the anchor facing downward, it being noted that the bore whose mouth is shown facing downward in the view is internally threaded at some distance from its exposed outer end;
FIG. 2 is a perspective view of the invention showing the other end, which is normally imbedded in concrete; and,
FIG. 3 is a side elevational view of the invention.