The one-piece, open-end wrenching head includes two substantially equal-length jaws with a throat recess therebetween. The jaws respectively include driving surfaces spaced apart a distance slightly greater than the across-flats dimension of an associated hexagonal fastener, with each driving surface having a length no greater than the length of one of the flat sides of the associated fastener and having a serrated region thereon. The distance from the deepest part of the throat to an imaginary line connecting the distal ends of the jaws is approximately 0.86 times the across-flats dimension of the fastener.