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. KR15YC).

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.