This R-8 style relay valve fits Mack air brake systems and is built as a replacement for various Mack applications. Mounted near the brake chambers rather than at the treadle valve, it applies and releases air on demand, cutting down the lag common with valves positioned farther from the brakes. It ships packaged one per sell unit.Interchanges:20QE127920QE40220QE402R20QE410R745-287347745-289395Mack 20QE410LRV-5617FeaturesR-8 style relay valveSell pack: 1 EACHFits Mack universal applicationsTech SpecsSell pack: 1 EACH