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Left to right: 3" 4lb shots, 2" 6oz dexterity balls, 2.25" 20oz Ironmind level II balls
Dexterity balls are spheres ranging in size from 1" to more than 3" and in weight from a few ounces to 6lbs or more. Typically used in pairs, the smaller balls are rotated in the hands to develop independent control of the fingers and for active recovery after strenuous grip work. These are what people usually think of as chinese meditation balls or baoding balls.
The larger balls can get quite heavy and are used to stretch and strengthen the hand in the most open positions. People looking to train this way often use javelin training weights or (for the heaviest work) small shot puts in place of the baoding balls. Some will even wrap the heavy balls in duct tape to add friction and make work with them even harder.