The Robo-Pro Series Sponge Wheel come in a "set of 4",  These wheels are made of high density sponge material, ensuring a thorough clean on any pool surface. Simply attach them to your pool cleaning robot and watch as they effortlessly glide across your pool floor, walls, and steps. With a life expectancy of 3-5 years, these wheels are a reliable and long-lasting.  Don't forget to remove your robot from the pool after each use and store in a shaded dry area to prolong the life of your wheels.