The Wheel Woolies Kit includes 3 sizes, each specifically designed for different jobs. The small brush is great for slim gaps that are difficult to get into, such as narrow spoke wheels. The medium brush can best be used in areas such as your vehicle’s engine, door jambs, air diffusers, etc. The large brush will effectively scrub deep within the wheels and the wheel walls of any automobile, no matter its size. The 18″ Brush in the B Kit has a smaller 1 3/4″ diameter brush head for aggressive use in smaller spaces compared to the 18″ Large brush which has a 4″ brush diameter.