This castellated nut is from the body parts section in the Rolls-Royce & Bentley parts catalogue for models built between 1956 to 1965.
This nut is for the track rod pins.
Whenever you fit a car part - or fix any material for that matter - using a combination of nuts and bolts, washers should always be used. It is not merely a cosmetic accessory, instead it actually performs two functions, the first being to protect the metalwork from being damaged due to the tightness of the nut, and secondly to provide a smooth, flat surface so that the nut and bolt stay done up tightly or as long as possible.
All our parts branded Prestige Parts have a 3 year warranty.