Generally, there are stainless steel products, such as centripetal balls of marbles.

Through the repeated rotation of hands, the functions of knuckles, wrists, palms, elbows and shoulders can be enhanced, and blood circulation can be promoted, which is beneficial to the brain and central nervous system.

Many people play with walnuts and iron balls. Practice makes perfect. One hand has two or even five balls, and a master can play with both hands at the same time.