This pair of Outdoor Activity Wheels enable safety when using the Nimbo Posterior Posture Walker (sold separately) outdoors. Designed to replaced existing front two wheels wheels, the existing back wheels on the Nimbo can remain in place for outdoor use or two pairs of the Outdoor Activity Wheels can be purchased.The wheels have a larger diameter of 228mm (9\"), compared to the standard Nimbo wheels, ensuring the Nimbo remains sturdy on a variety of outdoor floor surfaces. Suitable for medium, large, X large and XX large Nimbo Walkers. Please note the wheels will increase the height of the Numbo by 25mm (1\").