Uniform velocity over the entire blade area is the most important criteria of efficient axial flow fan design. To produce a uniform velocity through out its length, a fan blade must vary from a thin tip to a thick cambered root. Each point on the blade must have the proper combination of chord (Blade width) and angle. This results in a great deal of twist in a properly designed blade, a shape impossible to produce by extrusion. The fan blades are jig-formed to provide the complex contour needed for high aerodynamic efficiency.