from a horse toy to a training aid, stacy's activity ball is a versatile tool for a wide range of riders. the larger sizing of this ball makes it perfect for larger horses. this ball should not be used with shank bits because it may bounce up and jar the shanks. the ball's circumference should be approximately 124" when fully inflated with a height of 39". please inflate fully to help prevent horse from biting ball. supervision is recommended at all times. red.