Round wire: diameter 0.03mm-10.0mm
Flat wire: thickness 0.2mm-1.0mm, width 0.08mm-40.0mm

Thermocouples

Low cost thermocouple materials can be used up to 1100°C (type K, Nicr/NiAl) or 1200°C (type N, nicrosil/nisil).

Above this temperature these materials have only a short life so more expensive platinum/rhodium (Pt/Rh) thermocouples must be used eg types R, B, 20/40.

Round wire: diameter 0.020mm-10.0mm

Flat wire: thickness 0.025mm-4.0mm, width 0.040mm-4.0mm

Heating Elements
Fecral resistance wire can be used up to 1300C. Above this temperature more expensive silicon carbide(SiC) elements are used. And from1500°C to1600°C a higher grade of silicon carbide is required.
The cost of using MoSi2 elements is increased by their need for low voltage transformers and a current limiting control system.
1800°C graphite(C), molybdenum(Mo) or zirconia(Zro2) elements are used.