A pipe wrench is any of several types of wrench that are designed to turn threaded pipe and pipe fittings for assembly (tightening) or disassembly (loosening) Pipe wrench also known as the Stillson wrench is an adjustable wrench (spanner) with hardened serrated teeth on its jaws The hard teeth bite into the softer metal of the round pipe, and provide the grip needed to turn a pipe, even against fair resistance The design of the adjustable jaw, which permits a certain amount of intentional play out of square, allows it to bind on the pipe, with forward pressure on the handle pulling the jaws tighter. Two leaf springs, above and below the knurled adjusting knob, help unlock the jaw when pressure on the handle of the wrench is released Pipe wrenches are not intended for regular use on hex nuts or other fittings