A wrench is a tool that is used to apply torque to tighten or loosen a nut or bolt (fastener). Selecting the appropriate wrench depends on the design and size of the fastener. Selection can also depend on the space available around the fastener.
Wrenches are available in standard (SAE) and metric measurement standards. There are many different wrench types, each designed for a particular purpose, use and operation.
The quality and treatment of the metal used to manufacture wrenches affect the cost. Higher quality and therefore more costly wrenches are typically made from chromium-vanadium alloy tool steels and are often drop-forged. They are frequently chrome-plated to resist corrosion.