Thermocouples are available in different combinations of metals or calibrations. The most common are the “Base Metal” thermocouples known as Types J, K, T, E and N. There are also high temperature calibrations - als known as Noble Metal thermocouples - Types R, S, C and GB.
K Type Thermocouples are known as general purpose thermocouple due to its low cost and temperature range.
This high temperature wire/thermocouple is produced using a wide range of materials, and is available with PVC, FEP, TFE, PFA, Fiberglass, and Ceramaflex insulation. However, if you see it referenced by “type” on a spec sheet, the description is referring to the kind of metal alloy used for the wire’s conductor:
Type E = Chromel/Constantan
Type J = Iron/Constantan
Type K = Chromel/Alumel
Type N = Nicrosil/Nisil
Type T = Copper/Constantan
When an “X” follows the letter indicating which alloy was used in the cable, the cable is extension grade. In these cases, the types of cable are listed as Type EX, Type JX, Type KX, Type NX, or Type TX.