NON-LOOSENING DESIGN: These locking nuts have nylon inserts so when the nut is tightened the thread cuts into the nylon, holding it firmly in place, preventing loosening in high vibration applications. 6 POPULAR SIZES: Contains an assortment of 6 of the most popular sizes for a wide range of professional or home uses. ANTI-RUST DESIGN: The locknuts are zinc-plated, giving them enhanced rust resistance and longevity.