What shape does an Allen wrench have?

An Allen wrench, also known as a hex key, has a hexagonal shaft shape. This design features a six-sided cross-section, which allows the wrench to fit snugly into the corresponding hexagonal recess of fasteners such as screws and bolts. This shape provides a greater surface area for torque application compared to other shapes, allowing for more efficient turning and access to tight spaces. Additionally, the hexagonal design allows for better grip and leverage, reducing the likelihood of stripping the screw head when applying force. This makes the hexagonal shape essential for tools intended for mechanical work and assembly in various applications, especially in the automotive and furniture industries.

The other shapes listed do not apply to Allen wrenches. A round shaft would not provide the necessary engagement with the fastener, a square shaft is characteristic of a different type of tool, and a flat shaft, like that of a screwdriver, is not suitable for hexagonal fasteners.