The Mikasa P850 8.5 4 Square Rubber Playground Ball is a 8.5 diameter ball with a Premium Rubber Cover. 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.