A hook wrench, also known in Great Britain as a hook spanner or a C-spanner, is a hand tool that consists of a flat handle that ends in a hook. The hook may be unmovable or it may be hinged to allow the wrench head to fit around parts of varying sizes. A hook wrench is used to tighten, loosen or hold machinery components that are round but also notched or multi-faceted, such as lock nuts and pipe fittings. Due to the fact that it is available in a range of different sizes and often has an adjustable head, it is a highly flexible tool that can be used to adjust parts of varying circumferences.
In most cases, hook wrenches are made from highly durable chrome or carbon, stainless, or tool steel. Their handles may be coated with a rubber or plastic sleeve to improve the user’s grip and comfort. Commonly available models range in length from around 4 inches (10.16 cm) up to 13 inches (33.02 cm). Depending on the size of the individual model, a hook wrench is capable of adjusting components with a diameter as small as 0.6 inches (1.52 cm) and as large as 8 inches (20.32 cm). It can range in weight from approximately 0.05 pounds (22.68 g) up to approximately 3 pounds (1.36 kg).
Whether a hook wrench’s head, or hook, is fixed in place or adjustable, the inner side of its curve usually ends in a small, downward pointing tooth or claw. When the wrench is placed around the part it is being used to manipulate, this tooth fits into the part’s notch — as with a crimped lock nut — or grasps onto one of its facets — as with a beveled pipe fitting. As the wrench is turned, the tooth prevents the head from slipping out of place, allowing the user to adjust the part quickly and efficiently.
The hook wrench is commonly used to construct and repair machinery that incorporates pipes or other round parts that are joined together by nuts, retaining rings, or other couplings. This type of configuration is often found in plumbing and sanitation systems as well as dairy, refrigeration, and heating equipment. Hook wrenches are also useful in adjusting bearings, which are commonly found in products and machinery with moving parts. These tools are widely available on the Internet and from hardware and home improvement shops as well as industrial suppliers.