# How to read a Denso spark plug reference

> A Denso code encodes the electrode material, thread & seat, heat range, reach and gap. Here is how to decode it.

A Denso reference such as **IK20** or **W20EPR-U11** is read from the front: an optional **material prefix**, then the **thread letter**, the **heat-range number**, and finally the **type / reach / gap**.

## 1. Prefix — electrode material

- **I** / **V** — iridium (Iridium Power / Iridium Tough)
- **P** — platinum
- **S** / **F** — super-ignition iridium (fine tip)
- **D** — double-needle iridium
- **no prefix** — nickel (standard)

## 2. Thread letter — thread & seat

LetterThreadØ / seat
WM14×1.2514 mm · flat (gasket), 13/16" hex
KM14×1.2514 mm · flat (gasket), 5/8" hex
XM12×1.2512 mm · flat (gasket)
Q / TM14×1.2514 mm · taper seat
M / AM18×1.518 mm · flat (gasket)

## 3. The number — heat range

The digit is the **heat range**: for Denso, **higher = colder**, lower = hotter. It is relative to the Denso scale (e.g. 16 is hotter than 20 than 24).

## 4. Remaining letters

- **R** — built-in resistor (suppressed)
- **U** — U-groove ground electrode
- **P** — projected insulator / platinum tip
- **E** — long reach (19 mm)
- **L** — resistor / long-life variant

## 5. Suffix — reach & gap

A trailing number after a dash is the pre-set **gap** in tenths of a millimetre (**-11** = 1.1 mm, **-8** = 0.8 mm). Some families code the reach here too.

## 6. 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 Denso spark plug reference](https://www.thesparktwin.com/en/guide/nomenclature-denso/) — TheSparkTwin*