This is a J-type thermocouple wire with black PVC insulation, which is good up to about 105 C or 221 F. This J-type thermocouple wire can be used to make your own type J thermocouples for a wide range of applications, or to make your own J-type extension wire. The iron / constantan wire is made to standard J-type thermocouple specifications. This is a stranded wire with 7 filaments, it is more flexible than a solid wire and therefore especially useful for J-type extension wires. It is sold in 10 yard increments,