NGK spark plug codes generally consist of six fields, which break down as follows:
| D | Size of the thread, pitch and hex |
|---|---|
| P R | The contruction shape or feature |
| 9 | Heat Rating |
| E | Thread Reach |
| A | Type of firing end contruction |
| - | - |
| 9 | Spark Plug Gap - not all plugs show this |
Some fields (e.g., the second field) are optional, and some fields may have multiple letters.
| Thread Diameter | Pitch | Hex | |
|---|---|---|---|
| A | 18mm | 1.50mm | 25.4mm |
| B | 14mm | 1.25mm | 20.8mm |
| C | 10mm | 1.00mm | 16.0mm |
| D | 12mm | 1.25mm | 18.0mm |
| E | 8mm | 1.00mm | 13.0mm |
| G | PF 1/2" pipe | 23.8mm | |
| AB | 18mm | 1.50mm | 20.8mm |
| BC | 14mm | 1.25mm | 16.0mm |
| BK | 14mm | 1.25mm | 16.0mm |
| DC | 12mm | 1.25mm | 16.0mm |
| BM_A | 14mm | 1.25mm | 19.0mm |
| BPM_A | 14mm | 1.25mm | 19.0mm |
| CM_6 | 10mm | 1.00mm | 14.0mm |
| Feature | |
|---|---|
| M | Compact(hex 19mm) |
| L | Short |
| P | Projected insulator |
| R | Resistor |
| U | surface or semi-surface discharge |
| Z | inductive suppressor |
Letters may be combined
Back to Symbols
From 2 (hot) through to 14 (cold) - for more information see Hot and Cold Plugs.
Back to Symbols
| Thread Reach | |
|---|---|
| E | 19.0mm |
| H | 12.7mm |
| L | 11.2mm |
| EH | Part Threaded |
| Total reach = 19.0mm | |
| Thread = 12.7mm | |
| BM_A | 9.5mm |
| B_LM | 9.5mm |
| CMR_A | 9.5mm |
| Firing and Construction | |
|---|---|
| C | short ground electrode |
| F | tapered seat |
| G | fine-wire center electrode, nickel |
| J | 2 ground electrodes (special shape) |
| K | 2 ground electrodes (Toyota) |
| -L | half heat range |
| -LM | insulator length: 14.5mm |
| M | insulator length: 18.5mm |
| -N | special ground electrode |
| P | platinum tip |
| Q | 4 ground electrodes |
| R | delta ground electrode |
| S | super copper core |
| T | 3 ground electrodes |
| V | fine-wire centre electrode, gold palladium |
| VX | platinum centre electrode |
| W | tungsten electrode |
| X | booster gap |
| Y | v-grooved centre electrode with extra projection |
| Spark Gap (pre-set) | ||
|---|---|---|
| 8 | 0.8mm | 0.032" |
| 9 | 0.9mm | 0.036" |
| 10 | 1.0mm | 0.040" |
| 11 | 1.1mm | 0.044" |
| 13 | 1.3mm | 0.050" |
| 14 | 1.4mm | 0.055" |
| 15 | 1.5mm | 0.060" |
| 20 | 2.0mm | 0.080" |
| none | Standard Gap | |
Heat rating and heat flow path of NGK Spark Plugs
It has a larger surface exposed to the combustion gasses, it dissipates heat slowly, its firing end heats up quickly
It has a smaller surface exposed to the combustion gasses, it dissipates heat quickly, its firing end does not heat up quickly
The lower the number hotter the plug
The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.
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EN