NIST, National Institute of Standards and Technology, U.S. Department of Commerce
NIST Temperature Scale Database (SRD 60), Version 3.0

Table I. Letter designations, compositions, and trade names of single-leg thermoelements:

Thermocouple Data
Letter designations, compositions, trade names
Designation Compositions and Trade Names
...N Denotes the negative thermoelement of a given thermocouple type.
...P Denotes the positive thermoelement of a given thermocouple type.
BN Pt-nominal 6% Rh.
BP Pt-nominal 30% Rh.
EN or TN Nominally 55% Cu, 45% Ni, constantan: Cuprona, ThermoKanthal JNb, Advancec; often referred to as Adams constantan.
EP or KP Nominally 90% Ni, 10% Cr: Chromeld, Tophela, ThermoKanthal KPb, T-1c.
JN A Cu-Ni alloy similar to, but usually not interchangeable with, EN and TN; SAMA specification.
JP Nominally 99.5% Fe: ThermoKanthal JPb.
KN Nominally 95% Ni, 2% Al, 2% Mn, 1%Si.: Alumeld, Niala, T-2c, ThermoKanthal KNb.
NN Nominally 95% Ni, 4.5% Si, 0.1% Mg, nisil.
NP Nominally 84% Ni, 14% Cr, 1.5% Si, nicrosil.
RN, SN High-purity platinum
RP Platinum-13% rhodium
SP Platinum-10% rhodium
TP High-purity copper

Note: All compositions are expressed in percentages by weight.

a Trademark - Carpenter Technology Corporation.
b Trademark - Kanthal Corporation.
c Trademark - Driver-Harris Company.
d Trademark - Hoskins Manufacturing Company.