There are several types of thread-rolling machines, each designed for specific applications and workpiece sizes. The most common types include flat die thread rolling machines, cylindrical die thread rolling machines, and planetary thread rolling machines. Flat die machines are used for producing threads on flat surfaces, while cylindrical die machines are used for producing threads on cylindrical parts. Planetary machines are used for producing threads on large-diameter parts, such as pipes and shafts. The main differences between these machines are the type of die used, the method of feeding the workpiece, and the degree of automation.