Enclosed Sealed Surface Thermometer -50° to 110°C #309CEnclosed Sealed Surface Thermometer 50 to 110C #309C The 309 surface temperature thermometers are unilateral thermal sensors, which measure the temperature of the contact surface. These instruments are fully enclosed to protect the bimetal from dirt and dust. Accuracy of the thermometer is 2% of full scale range. 2 inches in diameter and weigh only 1 ounce. The bimetallic sensor is designed to permanently retain its calibration. 50 to 110C Fully