97-3106A-18-4S Circular Connector, 97 Series, Straight Plug. The 97-3106A-18-4S is a 4-contact Circular Connector, 97 series, straight plug, 18-4 insert arrangement, solid backshell and socket contact. Connector component is fabricated from high grade aluminium alloy, with a conductive cadmium-plated finish and an olive drab chromate after-treatment.