# How to read a Torch spark plug reference

> Torch codes combine a shell letter (thread & reach, ISO sizes), a heat-range number, a resistor mark and design-symbol letters for the tip and electrode material. Here is how to read them.

A Torch code such as **K6RTC** or **DR15YC** is read left to right: the **shell** letter(s), the **heat range** number, an **R** for resistor, then the **tip / electrode** design symbols and an optional **-gap** suffix. Torch shells follow ISO dimensions (M14×1.25, M12×1.25, M10×1.0, M18×1.5).

## 1. First letter(s) — shell (thread & reach)

The leading letter(s) identify the metal shell — the **thread diameter and reach** — to ISO standards (14 mm, 12 mm, 10 mm or 18 mm thread). Compare with the equivalents listed on the page to confirm the exact fitment.

## 2. The number — heat range

The digit is the **heat range** (relative to Torch): a lower number is hotter, a higher number colder.

## 3. R — resistor

An **R** means a **built-in interference-suppression resistor** (e.g. K**R**15YC).

## 4. Design symbols — tip & electrode

Torch marks the design with letters (official « Design Symbols »):

- **C** — copper-core centre electrode
- Yttrium-alloy centre electrode
- two ground electrodes
- **IQ** — V-grooved centre electrode
- iridium centre electrode
- double iridium (pin-to-pin)
- **IU** — iridium centre electrode & U-grooved ground electrode
- projected tip / 5 mm ignition position, shell-guide extension

## 5. Spark gap (suffix)

A trailing number after a dash is the pre-set **gap** in tenths of a millimetre (e.g. **-11** = 1.1 mm, **-13** = 1.3 mm).

## 6. Tightening torque

Torque depends on the seat, thread diameter and cylinder-head material. Flat seat (with gasket): 10 mm 10–15 N·m (iron) / 10–12 (alu), 12 mm 15–25 / 15–20, 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 Torch spark plug reference](https://www.thesparktwin.com/en/guide/nomenclature-torch/) — TheSparkTwin*