Mikasa 8.5" 4 Square Rubber Playground Ball Model: P850 4-Square? When you play with this 8.5" Mikasa, it's more like 8-Square or 16-Square. Your games get so big it can take nearly an entire recess to reach the top. The P850 is the preferred ball of Playground Kings and Queens. 1-Year Warranty. - 8.5" Diameter - Four Square Model - Premium Rubber cover (no latex) Balls may be shipped deflated and must be inflated before using.