This is nyloc nut used in place of a nut GHF222 and spring washer GFK3322

Places used, exhaust clamps at the differential bracket, on the steering rack "U" clamps, holding the rear backplates on to the radius arm, on the transmission studs, engine mountings

This locking nut 5/16" UNF and is plated in zinc passivate to help resist corrosion