Which tool is primarily used for creating internal threads?

The primary tool used for creating internal threads is a tap. Taps are specifically designed for cutting threads inside a pre-drilled hole, allowing for fasteners such as screws and bolts to be securely installed. They come in various sizes and thread types, making them versatile for different applications in machining and manufacturing.

While other tools have their specific functions, they do not create internal threads. A reamer is used to improve the finish or dimensional accuracy of an already drilled hole, not for threading. A drill creates holes but is not meant for threading; it removes material to make a hole and has a different cutting geometry. A milling cutter is used for shaping or machining flat surfaces, slots, or other shapes but does not cut threads internally like a tap does. Thus, the tap is the correct tool for generating internal threads efficiently and accurately.