Which tool is primarily used to shorten the free edge of the nail quickly?

The tool primarily used to shorten the free edge of the nail quickly is nail clippers. Nail clippers are designed with a specific mechanism that allows them to cut through the nail with precision and speed, making them ideal for quickly shortening nails before further shaping is done with other tools, such as a nail file.

In contrast, a nail file is generally used for smoothing and refining the edges after the nail has been trimmed, rather than for cutting it down in length. A metal pusher is utilized for pushing back the cuticles and does not serve any function in shortening the nail. Cuticle nippers are specifically made for trimming excess cuticle skin, rather than altering the length of the nail itself. Therefore, nail clippers are the most efficient and effective choice when the objective is to shorten the free edge of the nail rapidly.