Palmwood cylinder with milled grooves, containing coils of insulated bobine thread. Wounded in a special way with white silk, for large inductance and capacitance and low resistive load. The turns are finished to terminal blocks with split pins. The NRI made these coils for use in its own devices and for amateur radio homebuilders and small traders. They were used for circuit and antenna coils of radio receivers between 300 / 600m and 1,000m. The coils gave low attenuation and better tuning.