Which tool is used to tighten the set screw at the base of the drill stop?

The correct tool for tightening the set screw at the base of the drill stop is the Allen wrench. This is because set screws typically feature a hexagonal socket (also known as a hex head) design, which means they require an Allen wrench, also known as a hex key, for proper engagement. The Allen wrench fits precisely into this type of screw, allowing for effective torque application.

Other tools listed, such as a Phillips or flathead screwdriver, are designed for screws with corresponding heads—like slotted or cross-shaped screw heads—and would not be able to grasp a set screw effectively. A torque wrench, while also a crucial tool for applying a precise amount of torque, is not suitable for a set screw that requires a hex engagement and is primarily used for torque specifications on fasteners like bolts and nuts. Hence, the Allen wrench is specifically designed for the task, making it the appropriate choice in this context.