Choose the ball of your favorite tennis stars with the Wilson US Open Tennis Balls. Since 1978, the US Open Tennis Ball has been the official ball of the Open, and now it can be your top choice. USTA and ITF approved for competitive play, the US Open ball is created with the ultimate in tex/tech industries felt and is available in Regular Duty for play on clay and indoor courts and Heavy Duty for matches on courts at elevations of above 3000 ft. FEATURES: Official US Open Tennis Ball since 1978 Approved for competitive play by the USTA and ITF Created with superior tex/tech industries felt Regular Duty tennis ball is perfect for the ultimate performance on clay and indoor courts Heavy Duty tennis ball is the optimal choice for courts above 3000 ft. in altitude Model: WRT1071 and WRT1073