Upper Conn: Double Banana Jack Material: Brass per QQ-B-626, Alloy 360, ¨ö Hard. Finish: Nickel plated per QQ-N-290, Class 2, 200 to 300 microinches. Insulation: Polypropylene molded to Banana Jack bodies Marking: ¡°POMONA ELECTRONICS CALIF.¡± ¡°MODEL 1823.¡± Lower Conn: Same as Upper Conn.