An Allen key is typically a small, L-shaped metal bar with a hexagonal cross-section. The two ends of the “L” shape are of different lengths, providing a short arm and a long arm. This design offers two primary uses: the short arm provides better torque for tightening or loosening fasteners, while the long arm allows for access to fasteners in deep or recessed areas. The hexagonal shape of the key fits snugly into the hexagonal socket of the corresponding fastener, reducing the likelihood of slipping and stripping the fastener head.