Which component is specifically noted as a part of a lathe machine threading mechanism?

In the context of a lathe machine's threading mechanism, the spindle gear plays a crucial role. The lathe relies on the spindle gear to control the rotation of the workpiece, which is vital for creating threads. When cutting threads, it is necessary for the workpiece to rotate at a precise speed that matches the movement of the cutting tool. The spindle gear helps achieve this synchronization, ensuring accurate and consistent thread profiles.

While other components like the reverse gear and lever, as well as the change stud gear, are essential in various aspects of lathe operation, they are not specifically highlighted as core components of the threading mechanism. The reverse gear and lever are generally used for changing the direction of rotation, which may assist but is not directly involved in forming threads. The change stud gear aids in altering the gear ratios, which affects the feed rate but is not as directly related to threading. Hence, among the options provided, the spindle gear is the most essential component specifically tied to the threading process in a lathe machine.