Arvid Nilsson 18020000 is a DIN 985 stainless/acid-resistant A4-80 hex lock nut with a nylon insert and wax coating, in M20 thread with a 2.5 mm pitch and a 30 mm wrench flat. The nylon ring provides self-locking action to resist vibration loosening and the wax lowers installation torque scatter. Typical applications include marine, water-treatment and outdoor structural assemblies requiring reliable stainless fastening.