A wrench (or spanner outside of North America) is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning.
In Commonwealth English (excluding Canada), spanner is the standard term. The most common shapes are called open-ended spanner and ring spanner. The term wrench is generally used for tools that turn non-fastening devices (e.g. tap wrench and pipe wrench), or may be used for a monkey wrench - an adjustable spanner.
In North American English, wrench is the standard term. The most common shapes are called open-end wrench and box-end wrench. In American English, spanner refers to a specialised wrench with a series of pins or tabs around the circumference. (These pins or tabs fit into the holes or notches cut into the object to be turned.) In American commerce, such a wrench may be called a spanner wrench to distinguish it from the British sense of spanner.
Higher quality wrenches are typically made from chromium-vanadium alloy tool steels and are often drop-forged. They are frequently chrome-plated to resist corrosion and for ease of cleaning.
Hinged tools, such as pliers or tongs, are not generally considered wrenches in English, but exceptions are the plumber wrench (pipe wrench in British English) and Mole wrench (sometimes Mole grips in British English).
Wrenches and applications using wrenches or devices that needed wrenches, such as pipe clamps and suits of armor, have been noted by historians as far back as the 15th century. Adjustable coach wrenches for the odd-sized nuts of wagon wheels were manufactured in England and exported to North America in the late eighteenth and early nineteenth centuries. The mid 19th century began to see patented wrenches which used a screw to narrowing or widening the jaws, including patented monkey wrenches.
Other types of keys
These types of keys are not emically classified as wrenches by English speakers, but they are etically similar in function to wrenches.
Size is usually designated by dimensions such as across-flats distance (inscribed-hexagon size). In the 19th and early 20th centuries, it had been common to define the nominal size of the wrench according to the nominal size of the screw thread that it was meant to be used with. Modern practice uses a size designation based on across-flats distance, whether measured in metric or in inch units.