Hexagon Nylock Nut made to specification DIN 985. Stainless Steel Material to grade A2/70 which provides good corrosion resistant properties. 

Hexagon Nylock Nuts, Nylon Locking Nuts or sometimes called Nyloc Nuts are a type of self locking nut, fitted with a polymer insert. The nylon insert helps keep the nut from loosening and are used where vibration may impact the fastening. They are used with bolts and washers to join multiple components. 

When using stainless steel fixing it's important to use all stainless components and separate different metal types with a nylon washer.