Thread connection is widely used, but its anti-loosening problem has been plaguing everyone. There are many measures to prevent loosening, but from the comprehensive analysis of effect, process and cost, double nut connection is a widely used and reliable way to prevent loosening. However, there is no definite relationship between the anti-loosening effect and the tightening moment of the two nuts. Through the experiments on the experimental device of transverse vibration of fasteners under different pre-tightening forces, the relationship between the anti-loosening effect under different pre-tightening forces and the pre-tightening force between the two nuts is summarized. Based on the detailed study of the working principle, composition and characteristics of many kinds of test-bed at home and abroad, a transverse vibration test-bed for fasteners has been developed.

Thread refers to the spiral-shaped continuous bulge with a specific cross-section made on the surface of a cylinder or cone parent. Threads can be divided into cylindrical threads and conical threads according to their mother shape, external threads and internal threads according to their position, and triangular threads, rectangular threads, trapezoidal threads, serrated threads and other special shaped threads according to their cross-section shape (tooth type).

On the surface of a cylinder or cone, a continuous protuberance with a specified tooth profile is formed along a spiral line. Protrusion refers to the solid parts on both sides of the thread. Also known as teeth.

In mechanical processing, the thread is cut on a cylindrical axis (or inner hole surface) with a cutter or grinding wheel. At this time, the workpiece rotates around, the cutter moves along the workpiece axis for a certain distance, and the trace cut by the cutter on the workpiece is the thread. The thread formed on the surface of the outer circle is called the outer thread. The threads formed on the surface of the inner hole are called internal threads. The basis of the thread is the helix on the surface of the circular shaft. Generally, if the cross-section of the thread is triangular, it is called triangular thread; the cross-section is trapezoidal thread; the cross-section is sawtooth thread; the cross-section is square thread; the cross-section is circular arc thread and so on.

The anti-loosening experiment of twin nuts was completed on the lateral vibration tester of fasteners. The experiment mainly includes two aspects. On the one hand, the relationship between the tightening moment of the two nuts is analyzed experimentally. It is considered that the tightening moment of the two nuts is related to the tightening moment of the two nuts. The bigger the tightening moment of the two nuts is, the bigger the tightening force of the bolts is, but it is not a simple combination of the corresponding tightening force of the two tightening moments. The results show that the anti-loosening effect is better when the tightening moment of the upper nut is greater than that of the lower nut. In other words, the tightening moment of the upper nut plays a key role in the anti-loosening effect of the connection. Blind hole nut