129 Series, matched large glass probe, 4,000 Ohm resistance, ±2.0% tolerance, 25/85 BETA = 3518 126 Series and 128 Series Thermistors are designed for use as precision sensing elements where curve-matched interchangeability is required for precise temperature control and precision temperature indication. These highly reliable products consist of a matched pair of hermetically sealed thermistors and may be selected to tolerances only limited to the system’s capability available to test them.