The Ohaus ST320 IP67 3m 3-in-1 Plastic pH Electrode is compatible with ST400 and ST400M portable meters. The electrode has a plastic shaft that is durable and sturdy, but not recommended for usage at temperatures above 80˚C. The shaft provides moderate resistance to highly corrosive materials and organic solvents. The electrode has non-refillable gel, which means that no maintenance is required; however, the electrode must be replaced when contaminated.