FK-2 and FK-20 air outlets are single-layer adjustable louvered air outlets, and their blades and frames are common to FK-1 and FK-19 air outlets, respectively. This is often used as a return air vent. When used as a return air vent, it is often used with the FK-5 aluminum alloy filter. A multi-leaf halving control valve can be installed behind the air vent to control the air volume. The installation method is the same as FK-1; FK-19 air outlet. The difference between FK-2 and FK-20 is that the outer frame and blade size are different. FK-20 is a narrow frame window blade, the rest are exactly the same.