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). The Stillson wrench, or Stillson-pattern wrench, is the usual form of pipe wrench, especially in North America. The Stillson name is that of the original patent holder, who licensed the design to a number of manufacturers. The patent expired decades ago. Another type of wrench often used on pipes, the plumber wrench, is also called a pipe wrench in some places.
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. However, if a hex nut becomes rounded (stripped) so that it cannot be moved by standard wrenches, a pipe wrench can be used to free the bolt or nut, because the pipe wrench is designed to bite into rounded metal surfaces.
Pipe wrenches are classified by the length of the handle. They are generally available in any size from as small as 3 inches (80 mm) up to 48 inches (1,200 mm) or larger. They are usually made of cast steel. Today, aluminium might be used to construct the body of the wrench, although the teeth and jaw remain steel. Teeth and jaw kits (which also contain adjustment rings and springs) can be bought to repair broken wrenches, because that can be cheaper than buying a new one. Repairing a high-quality wrench can be more economical (taking into account the total cost of ownership) than either buying a new high-quality wrench or buying cheap wrenches repeatedly.
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