NGK Sparkplug Codes
This information is to help guide your choice of new
sparkplugs, or to determine the characteristics of the plugs
you already have.
The breakdown is like this:
[B] [CPR] [6] [E] [S] - [11]
There are six fields. Some, like the second field, are
optional. Fields may have multiple values.
- Field one: Thread diameter.
- A = 18mm
- B = 14mm
- C = 10mm
- D = 12mm
- Field two: Construction.
- C = hex size 5/8"
- K = hex size 5/8 with projected tip (ISO)
- M = compact type
- P = projected insulator type
- R = resistor
- SD = surface discharge for rotary engines
- U = semi-surface discharge
- Z = inductive suppressor
- Field three: Heat Range.
-
2 = hot, up to 10 = cold. (There is no 1 and it
doesn't go to 11)
- Field four: Thread reach.
- E = 19mm
- F = tapered seat
- H = 12.7mm (1.5")
- L = 11.2mm (7/16")
If this field is blank, an 18mm diameter plug has 12mm
reach, and a 14mm plug has a 9.5mm (3/8") reach.
- Field Five: Firing end construction.
- A, B = special design (no details given)
- C = special ground electrode
- G = racing use
- GV = racing use V type
- H = half thread
- K = 2 ground electrodes for certain Toyotas
- L = half heat range
- LM = compact lawn mower type
- M = 2 ground electrodes for Mazda rotary engine
- N = special ground electrode
- P = platinum tip (premium)
- Q = 4 ground electrodes
- R = delta ground electrode for BMW
- S = standard 2.6mm centre electrode
- T = 3 ground electrodes
- V = fine-wire centre electrode, gold palladium
- VX = platinum tip (high performance)
- W = tungsten electrode
- X = booster gap
- Y = v-groove centre electrode
- Field Six: (after the dash) Electrode gap.
- 8 = .032"
- 9 = .036"
- 10 = .040"
- 11 = .044"
- (12 isn't in use)
- 13 = .050"
- 14 = .055"
- 15 = .060"
- 20 = .080"
Resistor plugs are used for two reasons:
- They cut down electrostatic interference.
-
They provide a sharper "edge" to the voltage
spike, making for a stronger, shorter spark. On high RPM
motors, this is important.
The projected insulator simply describes the shape of the
plug head. A projected insulator sticks out a little further
into the combustion chamber.
You can reach NGK at 800-855-8151(?) or 714-855-8278
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