What should you use to remove a sunken bolt?

Using an allen wrench is the correct approach for removing a sunken bolt, especially if the bolt has an internal hexagonal socket. This type of fastener requires a specific tool that fits into the recessed area of the bolt head, allowing for effective torque application without risking damage to the bolt or surrounding material. An allen wrench is designed for this purpose, providing a snug fit that minimizes the likelihood of stripping the bolt.

The other tools mentioned, while useful for various tasks, do not fit the requirements for sunken bolts efficiently. A wrench is typically used for external nut or bolt heads, while pliers can grasp surfaces but are not ideal for exerting the torque needed for bolts, particularly if they are sunken and require precise engagement. A screwdriver is meant for screws with a slotted or Phillips head and would not work on a bolt that is designed for an allen wrench, making it ineffective for this specific task.