Adjustable wrenches are designed to provide a wide range of sizes in a single tool and are a convenient wrench for service and repairmen, linemen, etc. They are not intended to replace fixed opening wrenches for production or general service work. Properly used, this wrench tightens and loosens a wide range of nuts and bolts with light duty needs.
Adjustable wrenches come in many sizes and are typically measured by overall length of the wrench (example 6″ up to 15″). When larger wrenches are required we recommend use of a box end wrench because it will perform better with the higher torque requirements of larger nuts and bolts.
Do not use an adjustable wrench to free a “frozen” nut or to final tighten a nut. Never pull on a loosely adjusted wrench. Never use a hammer or extension on this wrench. Proper use of adjustable wrenches will protect your hands and the wrench from damage due to sudden failure (i.e. the wrench breaks).
Source: Hand Tools Institute