The tool that is commonly used for shaping nails during a manicure is the nail file. A nail file is specifically designed to smooth and shape the edges of the nails, allowing for precise control over the length and contour. It can be made from various materials, such as emery, glass, or metal, each providing different textures that can create different finishes on the nail edges.
The other tools mentioned serve different purposes in the manicure process. For example, cuticle nippers are used to trim excess cuticle and hangnails, while a nail buffer is used to polish the nail surface and add shine. Nail polish remover is a solvent used for removing nail polish but does not contribute to shaping the nails. Thus, while all these tools are important for a complete manicure, the nail file uniquely serves the critical function of shaping the nails.