Type K Magnetic Surface Thermometer ProbeThe primary difference between Type J and Type K thermocouples is the measuring range, and the sensitivity. Type K is the most common general purpose thermocouple with a sensitivity of approximately 41 V C. A wide variety of probes are available in its 50C to +900C 58F to +1652F range. Type K wire color standard is yellow (+) and red ( ). Type J has a more restricted range of 50 to +400C, but higher sensitivity of about 50 V C. Type J wire color