h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I believe there may be some confusion between adjustable wrenches and monkey wrenches. The tool discribed, with flat parrallel jaws, is an adjustable wrench, may be it just me, but I've always understood a monkey wrench to be a nickname for the stilson wrench.

Stilsons are the large wrenches used mainly by plumbers, the jaws are adjustable and have teeth. There is deliberately some 'slop' in the jaws which when applied correctly allows the the jaws to tighten as the wrench is turned, and the teeth bite into the nut. Although it is capable of rounding off the corners of nuts, it is also a useful tool for undoing nuts that have had the corner rounded off.