The big benefit of the Wheel Woolies is that they have a metal-free design which reduces scratches and brush dirty water splatter. Twisted wire spoke brushes are known to damage rims and create residue splatter due to their aggressive bristles. The soft, dense carpet fibers of the Wheel Woolies are 100% polypropylene, recyclable and chemical resistant. These fibers are great for holding in suds to transfer to the wheel. The three-piece kit is great for any wheel size opening.