The Hillman Group 4359 1/2-20 Stainless Steel Stop Nut (Nylon Insert) (3-Pack) Nylon Insert Lock Nuts have a captive undersized nylon washer that creates friction with the mating threads to prevent loosening Helps resist the effects of vibration and other forces Stainless steels are used for their corrosion resistance, high-temperature strength, scaling resistance and low-temperature toughness