Wilson WRT1073CS US Open Regular Duty Ball Case Make sure this fits. by entering your model number. The Wilson US Open Regular Duty tennis ball is the offical ball of the US Open since 1978. The US Open tennis ball is made with exclusive felt from Tex Tech Industries for superior playability, consistency, and durability. The yellow, regular duty felt is made for clay or indoor court surfaces. Also available are the Wilson US Open Extra Duty tennis ball for hard courts, Wilson US Open high Altitude tennis ball for all court surfaces over 3500 ft. elevation, or Wilson US Open Grass Court te! Must ship to school address or country club Only. US Open Regular Duty Ball Case Size - (See Description)_____Color - (See Description)