Please note this listing is for 2 balls. This item is based on traditional Chinese therapy theory. Through rotating the balls， you can improve manual dexterity and strength.<br /><br />Material: Chinese huang rosewood<br />Color: wood color<br />Diameter: about 40 mm/1.57''， 45 mm/1.77''， 50 mm/1.97''<br />SKU: 075-383 F