The bobbins, also calls inductancias, are the elements that change in his design probably more than any other component of the mentioned ones in this place. In his most elementary conception, a bobbin consists simply with a conductive thread wound on an insulating material. This type of designs gives birth to to the trasformadores, the bobbins of the electromagnetic relays, etcetéra, and in general to all those devices in which a self-induction is created by change of the current in a winding that produces magnetic lines and affects to another winding an electromotive force being created (f.e.m). across a magnetic field. One usually calls the self-induction also inductacia and that explains the generic name that the windings receive also.