[EN 12792:2003, 78]:in air diffusion there are three main categories of components:Air Terminal Devices (ATD’s)[EN 12792:2003, 78]:components of the installation which are designed for the purpose of achieving the predetermined movement of air into or from the treated space (e.g. grilles, diffusers, etc.) (Also see Air terminal device)complementary accessories to air terminal devices[EN 12792:2003, 78]:components of the installation which are used in conjunction with, and in some cases form an integral part of, the air terminal device for the purpose of achieving the predetermined profile or rate of flow into, or from, the air terminal device (e.g. air flow controllers, dampers, flow equalisers, baffles, etc.)fixing accessories for air terminal devices[EN 12792:2003, 78]:components of the installation which assist the fitting and fixing into place and/or maintenance of the air terminal devices and their complementary accessories (e.g. plaster frames, snap in fasteners, etc.)