The HI76409A/P are spare dissolved oxygen screwcap membranes designed especially for Hanna’s portable galvanic dissolved oxygen probes and sensors. The caps are constructed of durable ABS plastic with high density polyethylene (HDPE) oxygen permeable membranes. Each cap is easily filled with electrolyte and installed on the probe. The membranes separate the probes cathode and anode from the water being measured. Oxygen diffuses across the membrane and interacts with the galvanic system to produce a current proportional to oxygen concentration. Each cap is easily filled with HI7042 electrolyte and screwed on to the probe.