This air brake relay valve is designed for Mack applications. Mounted in the brake system near the chambers rather than at the treadle valve, it applies and releases air quickly to cut down on lag during braking. It ships as a single unit for one-for-one replacement on the truck.Interchanges:Mack 20QE461Mack 5396-KN28065LRV-3579FeaturesAir brake relay valveSold pack: 1 EACHTech SpecsSell pack: 1 EACH