Fasteners will eventually crack due to repeated stress cycles from peak to peak. The fracture usually occurs at the most vulnerable point of the fastener, which engineers call the 'maximum stress concentration area'. Once the microcracks are generated in the stress concentration and continue to be stressed, the cracks will rapidly expand, and the fasteners will undergo fatigue damage. Companies that manufacture industrial fasteners are constantly exploring new molding processes, and constantly designing and developing new manufacturing methods that can overcome the above-mentioned Achilles' heel. The most common locations for fatigue failure include the joint (ie the first loaded thread), the tooth root fillet, the thread, and the thread termination. As the processing industry has improved the fatigue strength through the development of better materials and production methods, the thread has become the weakest point of the fastener,and is currently the cause of the highest percentage of fatigue failure. The interrelationship between the designed stress variables and the performance characteristics of fasteners makes it a difficult task to set the standard of fatigue strength. At present, it is determined by the number of 'cycles to fracture' and the relative strength of the series of fasteners. It is a complicated process. 3.Corrosion Another machine screw manufacturers for bolt fracture is corrosion. Corrosion has many forms, including ordinary corrosion, chemical corrosion, electrolytic corrosion and stress corrosion. Electrolytic corrosion is: First, the fasteners are exposed and are corroded by various wetting agents such as rain or acid mist. These are electrolytes, which will cause chemical corrosion of the fasteners. Secondly, the materials of the fasteners are different. The electrolysis potential is different, the potential difference is easy to produce 'microbattery'.