A Nyloc ( nylon insert ) Nut is a torque prevailing nut, which uses a plastic/nylon insert to capture the bolt or screw providing a locking feature.Nyloc ( nylon insert ) Nuts are used in applications where vibration or motion could loosen or undo the nut.Also the Nyloc (nylon insert) Nut assists in sealing the bolt thread against seepage of oil, water, petrol, paraffin and other liquids.The Nyloc nut is available in a a variety of materials and finishes.