The variety of steepness and difficulty in River Stones builds children's coordination and balance. Rubber rim on the base of the stones helps prevent slipping and protects floors. Unlike other models that merely have a couple rubber feet, this rubber rim is continuous for increased stability & safety! River Stones are perfectly stack-able for practical storage, occupying only 15" x 15" x 5"! Set of 6. Set of 6 includes: • 3 Large stones w/ 15" sides (3-1/2"H) • 3 Medium stones w/ 11" sides (1-3/4"H)