... air volume,low noise 3.metal material(A3) 4.different size(4',6',8',10',12') industrial ducted fans ... impeller,and high-performance external rotor motor make our duct fan superior to others at the aspects of bulk, ... that impeller coule be driven by motor for small duct fans cubage, stable performance, high efficiency and durability ... safety for usage and easy to disassemble. Circular Duct Fan(IN LINE ...