The Penn QST 36 Red Felt Tennis Balls are Ideal for beginning players 8 and under playing on a 36' tennis court. The QST 36 Felt features a low compression core modifying the speed and bounce for greater control. Features:Low compression core with durable feltModified speed and bounce for greater controlPerfect for driveway play and outdoor courtsUSTA and ITF approved and endorsed by the PTRRed Ball for standard 36? tennis court sizeRecommended for ages 8 and underSpecifications:72 Balls with 12 balls per bag; 6 bags per caseThese Penn QST 36 Red Felt Training Tennis Balls are good for honing your skills at reduced speed, enabling you to master your approach and swing.