Threaded connection is widely used in modern large-scale production due to its strong load-bearing capacity, good interchangeability, and detachability. It has an important impact on the quality and safety performance of the whole machine. Threaded connection relies on the frictional force between the threaded pair and the connected parts to transfer the load, and the magnitude of the frictional force is directly related to the axial preload. If the axial preload is too large or too small, it will have an adverse effect on the threaded connection. If the axial preload is too small, the load-carrying capacity and anti-loosening performance of the threaded connection cannot meet the design requirements; if the axial preload is too large, the stress value of the thread contact surface is large, which is likely to cause mechanical damage such as thread deformation and sliding buckle. Reduce the reliability of threaded connections. Therefore, in order to ensure that the threaded connection meets the actual work needs of the connection, a reasonable axial preload range must be determined.