Dies are primarily used to cut which type of threads?

The primary purpose of dies is to cut external threads. Dies are tools that are used in a process called thread cutting, specifically designed to create uniform external threads on cylindrical materials, such as rods or bolts. When a die is rotated around a workpiece, it removes material to form the helical groove of the thread. This process allows for the efficient and precise manufacturing of screws and bolts, which are essential fasteners in various applications.

While there are tools available for cutting internal threads, such as taps, they serve a different function than dies. The other options, such as fine threads and pipe threads, describe specific standards or types of threads but do not represent the distinct purpose of the die itself, which is to create external threading. Thus, the use of dies is effectively focused on external threads, making this the correct choice in the context of the question.