# How to read a Champion spark plug reference

> Each letter and number in a Champion code is coded: resistor, thread diameter, reach, heat range, firing end and gap. Here is how to decode it.

A Champion reference such as **RN9YC** is read position by position, following Champion's official nomenclature.

## 1. Leading R — resistor

A leading **R** means a **built-in resistor** (suppressed), e.g. **R**N9YC. No thread letter is "R", so a leading R always marks the resistor.

## 2. Thread letter(s) — diameter & reach

LetterThread ØReach
A12 mm12.7 mmC14 mm12.7 mm
D18 mm11.7 mmF18 mm12.7 mm
J14 mm9.5 mm (taper seat)L14 mm12.5 mm (taper seat)
N14 mm19 mm (projected)P12 mm9.5 mm (taper seat)

Two-letter forms exist too (AX, CJ, DJ, DZ, EJ, MJ). The seat is **flat (with gasket)** unless the letter denotes a **taper seat** (e.g. J, L, P).

## 3. The number — heat range

The digit(s) give the **heat range**: lower = hotter, higher = colder. It is relative to Champion.

## 4. Firing end / design (final letters)

- **Y** — projected tip
- **C** — copper core
- **P** — platinum
- **G** — gold-palladium
- **LM** — lawn-mower type

## 5. Tightening torque

Torque depends on the seat, thread diameter and cylinder-head material. Flat seat (with gasket): 12 mm 15–25 N·m (iron) / 15–20 (alu), 14 mm 25–35 / 25–30, 18 mm 35–45 / 35–40. Taper seat: 12–14 mm 10–20 N·m, 18 mm 20–30. Always follow the value printed on the box.

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*Source : [How to read a Champion spark plug reference](https://www.thesparktwin.com/en/guide/nomenclature-champion/) — TheSparkTwin*