... 3.Long life time,low cost 4.Easy to maintenance Air diffuser(round,square,rectangle):1.Diffuser frame is made ... easily operated without taking the diffuser core out. 6.Foam gasket is sealed around the back of the frame as ... air leakage. 7.Standard sizes: 150x150, 225x225, 300x300, 375x375, 450x450mmThe outside view of the air diffusers:Round diffuserSquare diffuserRectangle diffuser HVAC Air Duct ...