Which tool is most appropriate for threading a round rod?

The most appropriate tool for threading a round rod is a die. A die is specifically designed for cutting external threads onto a cylindrical surface, which makes it perfect for creating threads on rods. When using a die, the round rod is inserted into the die, and as you turn the die, it cuts threads into the surface of the rod. This process allows for the secure attachment of nuts or other components by providing a standardized thread pattern.

In contrast, while a chisel is useful for shaping or cutting materials, it is not designed for creating threads. A drill is utilized for making holes rather than cutting threads, and while pliers are versatile tools for gripping and manipulating materials, they lack the capability to cut threads. Therefore, the die stands out as the correct choice for this specific task.