1.All models incorporate strong EC brushless motor for free speed control and lower energy consumption. 2.The fan casings are manufactured from pure ABS with straight design, it's double insulation. 3.The duct fan Adapted to any circumstance where strong ventilation is requested, such as metallurgy,light industry, chemical industryand so on. 4. Firm and safe installation: concave-convex design to both ends which can increase force of friction during duct connections.