A wrench is a commonly used tool for installation and disassembly, utilizing the principle of leverage to turn bolts, screws, nuts, and other threaded fasteners with openings or sockets. Wrenches are typically made from structural steel of carbon or alloy materials.
Wrenches usually have openings or sockets for gripping bolts or nuts at one end or both ends of the handle. When in use, external force is applied along the direction of the thread rotation on the handle to turn the bolt or nut.

Wrenches are generally divided into two types: fixed wrenches and adjustable wrenches. The former refers to wrenches with fixed sizes, while the latter refers to adjustable wrenches. 1. Fixed Wrench: Has fixed-size openings at one or both ends for turning nuts or bolts of a specific size. 2. Socket Wrench: Has working ends with hexagonal or dodecagonal holes at both ends, suitable for situations where the working space is limited and ordinary wrenches cannot be used. 3. Combination Wrench: One end is the same as a fixed wrench, and the other end is the same as a socket wrench, allowing for turning bolts or nuts of the same specification at both ends. 4. Adjustable Wrench: The opening width can be adjusted within a certain size range, allowing it to turn bolts or nuts of different specifications. This wrench features fixed jaws made with fine-toothed flat jaws; one end of the movable jaw is made flat; the other end is made with fine-toothed concave jaws; pressing down on the worm allows the movable jaw to be quickly removed and the jaw position to be changed. 5. Hook Wrench: Also known as a crescent wrench, used for turning flat nuts with limited thickness. 6. Socket Wrench: Composed of multiple sockets with hexagonal or dodecagonal holes, equipped with handles, extension rods, and various accessories, particularly suitable for turning bolts or nuts in very narrow or deeply recessed positions. 7. Allen Wrench: An L-shaped hexagonal rod wrench, specifically used for turning internal hex screws. The model of the Allen wrench is based on the size of the opposite sides of the hexagon, with bolt sizes having national standards. Uses: Specifically for fastening or disassembling round nuts on machine tools, vehicles, and mechanical equipment. 8. Torque Wrench: It can display the torque applied when turning bolts or nuts; or it will emit a light or sound signal when the applied torque reaches a specified value. Torque wrenches are suitable for applications where the size of the torque is clearly specified.