This specification covers the basic physical, chemical and performance requirements of reducers for use with various primer materials used on metal and plastic parts. The reducers are covered by specification numbers specific to the primer material with which they are used, described below. These reducers are used to adjust primer application viscosity, overall solvent evaporation for proper application, and film flow after application. The reducers may be individual solvents or blends of classes of solvents such as aromatic hydrocarbons, ketones and esters. Reducers approved under each specification are not interchangeable, and must be evaluated and approved for use with each specific approved primer material before addition to the applicable approved source list.