# U — Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class

For U, source document is ANSI and IEC Color Codes, verified against its source on 2026-08-19.

- **Type letter:** U _(verified: appears in the quote below)_
- **Source document:** ANSI and IEC Color Codes _(verified: appears in the quote below)_

## What the source says

> Extension Grade + + + U U NONE COPPER-LOW Connecting Wire for ESTABLISHED – COPPER R & S Thermocouples, – – Cu NICKEL Also Known as RX & SX Cu-Ni Extension Wire.

## Source

- https://assets.omega.com/pdf/test-and-measurement-equipment/temperature/sensors/thermocouple-probes/tc_colorcodes.pdf

Last verified: 2026-08-19. Review by: 2028-08-18.
Part of [Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class](https://referencesource.org/thermocouple-type-color-code-crosswalk/).