Threads are divided into internal threads and external threads, and the internal and external threads together form a screw pair. Both threaded connection and screw drive use threaded auxiliary parts to work, but the working properties of the two are not the same, and there are differences in technical requirements.

The thread that plays the role of connection is called the connecting thread, and the parts of the connecting thread are fasteners, which are required to ensure the strength of the connection (and sometimes tightness); the thread that plays the role of transmission is called the transmission thread, and the parts of the transmission thread are the transmission parts. The transmission accuracy, efficiency and service life of the pair for amusement equipment.

In the section through the thread axis, the profile shape of the thread is called the thread profile. According to different thread types, commonly used threads are triangular thread, rectangular thread, trapezoidal thread and serrated thread.

Commonly used thread types are ordinary thread, pipe thread, metric thread, rectangular thread, trapezoidal thread and serrated thread. The first three are mainly used for connection, and the last three are mainly used for transmission. The basic dimensions, characteristics and applications of various threads can be found in the mechanical design manual for amusement equipment.

According to the different rotation directions of the thread, the thread screwed in clockwise is called right-hand thread; the thread screwed in counterclockwise is called left-hand thread. The rotation direction of the thread can be judged with the right hand: as shown in Figure 2-69, extend the right hand, the palm is facing you, the four fingers are close together and parallel to the axis of the screw, and point in the direction of screwing in.

If the rotation direction of the thread is in the direction of the thumb Consistent, it is a right-hand thread, otherwise it is a left-hand thread. Generally, right-hand threads are commonly used. According to the number of helixes, it can be divided into single-thread thread (thread formed along one helix) and multi-thread thread (thread formed along two or more helixes, the helixes are equidistant in the axial direction) distributed).