Also available in a high-altitude version., Quantity: 24-Cans (72-Balls) , Item #: 601345-Case Tennis Ball Cases - Merchant of Tennis - Canada's Experts Tennis Balls Pack 24 Cans 72 Balls Official ATP Tour Tennis Balls Case 24 Cans 72 Balls 635903 Dunlop ATP Extra Duty Tennis Balls Officially endorsed by the ATP Tour, this high altitude version of the Dunlop ATP Championship Extra Duty ball features the same durable extra duty cloth as the sea level ball but features a special high atitude core for e at altitudes above 4,000 feet (1,219 meters This super-premium ball features HD Pro Cloth and HD Pro Core for ultimate consistency and performance. The Dunlop ATP Extra Duty tennis ball is the official ball of the ATP Tour! The Extra Duty premium ball is used at the season-ending ATP NextGen Finals and Nitto ATP Finals The Dunlop ATP Premium Tennis ball is Official ball of the ATP World Tour.