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
| Letter | Thread | Ø / seat |
|---|---|---|
| W | M14×1.25 | 14 mm · flat (gasket), 13/16" hex |
| K | M14×1.25 | 14 mm · flat (gasket), 5/8" hex |
| X | M12×1.25 | 12 mm · flat (gasket) |
| Q / T | M14×1.25 | 14 mm · taper seat |
| M / A | M18×1.5 | 18 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.