ZDTP or ZDP (zinc dialkyl or diaryl dithiophosphate) – Widely used as an antiwear additive in engine oils to protect heavily loaded parts, particularly the valve train mechanisms (such as the camshaft and cam followers) from excessive wear. It is also used as an antiwear agent in hydraulic fluids and certain other products. ZDTP is also an effective oxidation inhibitor. Oils containing ZDTP should not be used in machines that employ silver alloy bearings.