Oakton WD-35802-19 Fluoride F- Glass Body Double Junction Ion-Selective Electrode, Saturated - 0.02 ppm Range Fluoride (F-) ion solid state sensor Double-junction electrode to protect silver wire contamination, and to help prevent clogging Glass body to resist higher temperatures, and for more effective sealing Outer reference area is silver-free to resist contamination Bayonet Neill-Concelman (BNC)-connected combination reference and measuring cell, for ease of use and to provide a tight coaxial cable connection