1213U81 (WD-35640-80): Includes two complete membrane cap assemblies and 50mL of electrolyte solution.
1213U80 (WD-35640-72): Replacement membrane assembly consists of a preassembled membrane, membrane lock, O-ring, and cap. Simply screw replacement membrane assembly onto your probe.
7232C13 (WD-35640-79): Membrane installation tool lets you remove and replace membrane in the lab or field.