HI76409A/P is a replacement dissolved oxygen screw cap membrane designed for Hanna portable electroplated dissolved oxygen probes and sensors. The cap is made of durable ABS plastic with a high-density polyethylene (HDPE) oxygen-permeable membrane. Each cap is easily filled with electrolyte and installed on the probe. Membranes separate the probe cathode and anode from the water being measured. Oxygen diffuses across the membrane and interacts with the current system, producing an electric current proportional to the oxygen concentration. Each cap is easily filled with HI7042 electrolyte and screwed onto the probe.