In tools for thread cutting, which is best for plastic rather than metal?

The best tool for thread cutting in plastic rather than metal is the tap. Taps are specifically designed to create internal threads in pre-drilled holes, making them suitable for a variety of materials, including plastics. When cutting threads in plastic, it is vital to use a tool that minimizes stress on the material, and taps are designed to do just that by providing a clean and precise cut without excessively deforming the surrounding plastic.

In contrast, while other tools like a pipe cutter or reamer might technically be used in some plastic applications, they are not primarily designed for threading. A file is generally used for shaping or smoothing surfaces rather than for cutting threads. Hence, when it comes to creating threads in plastic, taps are the most efficient and effective choice.