An Allen wrench, also known as a hex key, is a small tool used to drive screws and bolts with a hexagonal socket. It typically has a simple L-shape design, which allows for easy handling and leverage. Allen wrenches come in various sizes to fit different hexagonal fasteners, making them versatile for many applications, including furniture assembly and bicycle repairs. These tools are commonly made from steel or other durable materials to withstand torque. Allen wrenches are often included with products that require assembly, such as furniture from IKEA or bicycles, ensuring users have the necessary tools for setup.