Adjustable Wrench  An adjustable wrench is often used where the exact size wrench is not available or when a large nut, such as a wheel spindle nut, needs to be rotated but not tightened.

An adjustable wrench. Adjustable wrenches are sized by the overall length of the wrench and not how  far the jaws open. Common sizes include 8, 10, and 12 inch.

An adjustable wrench should not be used to loosen or tighten fasteners because the moveable jaws can loosen their grip on the fastener, causing it to become rounded.