Please Refer to Third Picture for the Inflation Installation: first, put the horse ball into the ball cover, open the air plug, and start to inflate; When inflated to 31 inches, there is a large gap between the horse ball and the ball cover; When inflated to 35 inches, there is still some gap between the horse ball and the ball cover; When inflated to 40 inches, the horse ball and the ball cover fit completely, inflation is complete, plug in the air plug, and finally zip up Explosion Proof for Peace of Mind: you don’t have to worry about sudden bursts anymore; Thanks to our explosion proof rubber composite design that prevents the anti burst exercise balls from bursting violently when punctured; Instead, it deflates smoothly ensuring the safety and well being of your pets Comprehensive Kit for Horse: this set is ideal for pet owners who want to keep their horses entertained, as it comes with 1 toy ball, 1 ball cover, a plug, and a manual pump for ease