Which of the following describes correct pairs of tools?

The identification of tools and their corresponding shapes and functions is key to understanding their applications. An Allen wrench, also known as a hex key, is specifically designed to fit into hexagonal-shaped sockets, which allows for the turning of hexagonal screws and bolts. This correlation makes it a perfect match with the hexagon shape.

On the other hand, a flathead screwdriver, which features a simple wedge design, is intended for driving screws with a straight, flat slot in their heads. The design of the flathead allows it to fit seamlessly into these types of screws, enabling effective torque application.

Together, the flathead as a simple wedge and the Allen wrench as a hexagonal tool form a coherent and correct pair of tools with distinct shapes and functionalities. Thus, this pairing in the answer demonstrates an accurate understanding of how these tools relate to their respective forms and uses.