6.5 Interchangeability. The various products approved in accordance with MIL-DTL-81706 and listed on QPL-81706 provide equivalent coatings within each type and class. These coatings are equivalent insofar as performance of the chemical conversion coating is concerned, to the provisions of this specification, but are not interchangeable from a chemical standpoint; that is, different materials cannot be mixed. The materials from one supplier cannot be mixed or used to strengthen an existing solution from another material supplier. As the chemical coating materials are proprietary products, the ingredients, processes, the method of application (e.g., spray, brush, or immersion), and the equipment required for application of the coating may vary. Contractors and military activities must take this into account in acquisition, in the design of parts, and in the establishment of facilities. Detail drawing of parts requiring treatment in accordance with this specification should specify class 1A or 3, where applicable the required type, I or II, and any paint finishing systems required to meet the performance desired. If the coating class is not specified, class 1A is recommended.