Fender was trying to obtain a better string balance between poles. Having the pole pieces at different lengths would increase or lower the amount of magnetic field to the string. The core of the wound strings had less attraction and the pole pieces were slightly longer. The E & B strings had a larger outside diameter than the wound strings and the pole pieces were shorter. The magnets are in the pickups to magnetize the strings. As the strings move back and forth when plucked, an alternating current is generated and sent through the controls for volume and tone adjustment. Having less components in a model keeps production costs down and reduces the cost of each pole piece. It also allows for less inventory of several components.