1.Anut combination of a concave at upper and a convex at lower

2. When the upper nut is tightened to a reasonable torque, the lower nut willcompletely lock the bolt and achieve permanent anti-loosening.

3. A large contact surface of the lower nut and the bolt is designed to enhancethe anti-loosening performance and the tensile strength.

4.Indefinitely recycled.

5.Competitive price over theimported brands