An anchor fastener includes a head, a generally cylindrical shaft extending from the head, and a base at a distal end of the shaft. The shaft includes a helical thread on an outer surface and a self-drilling tip at its distal end adjacent the base. The base is frangibly connected to the distal end of the shaft by at least one web of frangible material separable from at least one of the base and the shaft under application of a force to the shaft.