This is a balance ball that allows you to perform a variety of workouts in one. 4 different diameter sizes. Product recommendation: Point 1: Suitable height ball size: Diameter 17.7 inches (45 cm), Suitable height under 59.1 inches (150 cm), Ball size under 21.7 inches (55 cm), Suitable height 59.1 - 65.0 inches (150 - 165 cm), Ball size diameter 2.9 inches (180 cm), point 2 cm); Suitable for use with sharp objects such as needles and nails. Slowly deflate the air. Point 3 Safety Specifications: Weight Limit up to about 220.5 lbs (100 kg) with hand pump