This specification sets forth the requirements for duplex, types E, J, K, N and T thermocouple wire, insulated with E-glass, S-glass, amorphous silica fiber or polycrystalline fiber. This specification presents the requirements for impregnated and non-impregnated fiber insulated thermocouple wire for normally accepted industrial use. The material shall be classified as follows: Class A-Duplex; Class B-Duplex; Class C-Duplex; Class D-Duplex; Class E-Duplex; and Class F-Duplex. Thermoelements shall be solid thermocouple grade materials with a smooth, bright finish and shall be fully annealed prior to insulating. Individual thermoelements shall be covered with a braid, or double wrap (one wrap in each direction) of glass fibers, a braid of glass fibers, or braid of fibers.