Baoding Chi-Gung Hand Exercise balls are widely used toto develop strong and nimble hands. They are said to stimulate chi energy flow through the hands and fingers, and to promote heath, and maybe even stave off arthritis. They’re also great as a warmup before any activity that requires a lot of manual dexterity. These balls are made of blackish jade stone, which displays a dark green marbled pattern. These have a great weight and solid feel. Approximately 2″ diameter.