A magnetic assembly structure includes a bobbin, an outer core, an inner core, and a gap spacer. The bobbin has first and second flanges. The bobbin has a passageway extending between the first and second flanges. The passageway has at least one crushable passageway rib and a channel wall parallel to the second flange. The outer core is positioned around the first and second flanges. The outer core includes an opening positioned near the first flange. The inner core is positioned in the opening and in the passageway. The gap spacer is positioned between the inner core and an inner surface of the outer core. The gap spacer and outer core are held in frictional engagement between the inner core and channel wall. The gap spacer defines a gap distance which is adjustable by replacing the gap spacer with one of having a different thickness. Adjusting the gap distance modifies the inductance.