Halo Trainer Can be used with any 55 cm to 65 cm exercise ball with adjustable levels of stability Heavy-gauge metal frame with thick, durable, ergonomic rubber grips Click connectors make it easy to assemble, and help make stability ball exercises more accessible and diverse for beginners and intermediate users Tested up to 800 pounds Balance and core exercise training aid for speed, agility, strength, power, running, football, volleyball, basketball, baseball, soccer and all other athletic, fitness, weight, or cross training