[EN 12792:2003, 79]:in air distribution there are three main categories of components:elements of distribution[EN 12792:2003, 79]:components for the purpose of ensuring a correct distribution of the air. (Also see Air duct, Ductwork components, Damper and valve, etc.)Air Terminal Units (ATU’s)[EN 12792:2003, 79]:equipment inserted into or added to the ends of ducts for the purpose of controlling one or more of various parameters such as velocity, pressure, flow rate and temperature. (See also Air Terminal Unit)accessories of distribution[EN 12792:2003, 79]:components ensuring the fitting and fixing in place of the elements of distribution and their inspection and maintenance. (See also Duct connection component, Door and Inspection panel, etc.)