Which tool is specifically designed for fitting hexagonal screw heads?

The tool designed specifically for fitting hexagonal screw heads is the Allen wrench. An Allen wrench, also known as a hex key, has a hexagonal cross-section that fits perfectly into the recess of hex screws, allowing for optimal torque and maneuverability. This design is particularly useful for screws commonly found in furniture assembly, bicycles, and machinery, where a compact tool is preferred.

Ratcheting screwdrivers and Phillips screwdrivers, while useful for various types of screws, are not tailored for hexagonal shapes. Ratcheting screwdrivers are designed to allow continuous turning without needing to lift the tool off the fastener, and Phillips screwdrivers are specifically made to engage with cross-shaped screw heads. An applicator tool is typically not used for fastening and does not have the appropriate design for hexagonal screws. Therefore, the Allen wrench is the clear choice for this task due to its specific shape and functionality.