A striking wrench is a sturdy hand wrench with a square, heavy handle and reinforced box walls. A sledgehammer is used to strike the handle of the wrench. This provides a much greater amount of torque than turning the wrench by hand. Striking wrenches are typically used to loosen rusted or otherwise frozen nuts and fasteners as well as to properly set fasteners in instances where large amounts of torque are required. The compact design makes striking wrenches ideally suited for applications where lack of space or clearance prevents the use of torque wrenches or other torque multiplication devices. They are commonly used in manufacturing areas, such as pipeline construction, shipyards and machine shops.
A well-made striking wrench must be durable enough to withstand repeated heavy impacts from a sledgehammer without breaking. Most are drop-forged from high-strength carbon steel, and heat-treated. The heat-treating process is tightly controlled in order to achieve a precise hardness. If the wrench is too soft, it could bend under pressure; if it is too hard, it could potentially shatter during use. Specialty striking wrenches made from non-sparking bronze and copper alloys are also available. They are typically used where combustible materials are present or where sparks from steel-to-steel contact could potentially cause unwanted damage. Non-magnetic wrenches are commonly used in power transmission facilities or other magnetically sensitive areas as well.
Striking wrenches come in both open end and box varieties, and in four-, six-, eight- or 12-point box patterns. Wrenches ranging in size from one inch (25.4 mm) to more than nine inches (22.9 cm) are available. Stinking wrenches are typically made with either straight or offset handles. In an offset striking wrench, the box is offset from the line of the handle. The offset allows the handle of the striking wrench to clear adjacent fasteners that would likely interfere with a straight handle wrench.
There are several dangers involved when using a striking wrench; proper safety procedures must be followed, and proper eye protection should be worn at all times. The wrench and sledgehammer should be inspected for cracks or damage before each use as well. Damaged wrenches or hammers should not be used and should be discarded, as flying metal from a breaking wrench can cause a great deal of damage and even injury. Often, for safety reasons a rope is used to apply pressure to the handle. This secures the striking wrench in place and prevents the wrench from slipping off the fastener. Care must also be taken when striking the handle of the striking wrench with the sledgehammer. The head of the sledgehammer should squarely impact the handle to provide maximum torque and prevent damage from a glancing blow.
Torque multipliers and hydraulic torque wrenches have largely replaced striking wrenches in many industries. They are generally safer to use, and unlike striking wrenches, can achieve a precise amount of torque. Striking wrenches do have some advantages over their modern replacements, however. They are generally less expensive to buy or maintain and are usually are easier to use. Striking wrenches are still widely used in oil and gas pipeline construction to tighten large flange fittings. There are also commonly used in shipyards, foundries and machinery repair shops.