The main purpose is to make the connecting lead of the coil winding compact, and the inner diameter of the winding circumference is slightly larger than the inner diameter of the stator, so as to prevent the loading rotor and rotor operation from damaging the coil. Except for the 2-pole motor, which needs to bind the 2-side ends of the sub-coil winding due to the large coil span, the other poles are generally only tied at one end of the coil winding connected with the outlet, and the other end does not need to be tied.