plaster frame[EN 12792:2003, 178]:separate mounting frame for an air terminal device designed to be incorporated into a plastered surface.secret (or concealed) fixing[EN 12792:2003, 178]:accessory by which an air terminal device can be secured to an opening without the outward appearance of screws or other fixing devices.’snap in’ fastener[EN 12792:2003, 178]:accessory used with an air terminal device as a fixing arrangement designed for the easy removal of the air terminal device for maintenance or cleaning. It can also be used to make the air terminal device compatible with a ceiling suspension system.(see also component of air diffusion)