Tennis ball shall have a uniform outer surface consisting of a fabric cover and shall be white or yellow in colour. If there are any seams they shall be stitch less. Size of the ball shall be more than 1.975 ounces (56.0 grams) and less than 2.095 ounces (59.4 grams) in weight. Each ball shall have a bound of more than 53 inches (134.62 cm) and less than 58 inches (147.32 cm) when dropped 100 inches (254.00 cm) upon a flat, rigid surface e.g., concrete.Ball Type 1 (fast speed) shall have a forward deformation of more than .195 inches (.495 cm) and less than .235 inches (.597 cm) and return deformation of more than .265 inches (.673 cm) and less than .360 inches (.914 cm) at 18 lb. (8.165 kg) load.
Ball Types 2 (medium speed) and 3 (slow speed) shall have a forward deformation of more than .220 inches (.559 cm) and less than .290 inches (.737 cm) and a return deformation of more than .315 inches (.800 cm) and less than .425 inches (1.080 cm) at 18 lb. (8.165 kg) load.
The two deformation figures shall be the averages of three individual readings along three axes of the ball and no two individual readings shall differ by more than .030 inches (.076 cm) in each case.
For play above 4,000 feet (1219 m) in altitude above sea level, two additional types of ball may be used. The first type is identical to Ball Type 2 (medium speed) as defined above except that the ball shall have a bound of more than 48 inches (121.92 cm) and less than 53 inches (134.62 cm) and the ball shall have an internal pressure that is greater than the external pressure. This type of tennis ball is commonly known as a pressurised ball.
The second type is identical to Ball Type 2 (medium speed) as defined above except that the ball shall have a bound of more than 53 inches (134.62 cm) and less than 58 inches (147.32 cm) and shall have an internal pressure that is approximately equal to the external pressure and have been acclimatized for 60 days or more at the altitude of the specific tournament. This type of tennis ball is commonly known as a zero-pressure or non-pressurized ball.
The third type of ball which is recommended for use for play on any court surface type above 4000 feet (1219 m) in altitude is Ball Type 3 (slow speed), as defined above.
