ISO 28741 Metric Thread Dimensions for Spark Plugs
Spark plug threads according ISO 28741 Road vehicles — Spark-plugs and their cylinder head housings — Basic characteristics and dimensions.
| Size | Major Diameter (mm) | Minor Diameter1) (mm) | Pitch (mm) | Tap Drill (mm) | Depth (mm) |
|---|---|---|---|---|---|
| M10 x 1.0 | 10.0 | 9.153 - 8.917 | 1.00 | 9.20 | 65 |
| M12 x 1.25 | 12.0 | 10.912 - 10.647 | 1.25 | 10.9 | 72 |
| M14 x 1.25 | 14.0 | 12.912 - 12.647 | 1.25 | 12.90 | 72 |
| M18 x 1.5 | 18.0 | 16.676 - 16.376 | 1.50 | 16.75 | 68 |
1) Tolerance class 6H.
The threads of spark-plugs and the corresponding tapped holes in the cylinder heads shall conform to ISO 68-1, ISO 261, ISO 965-1, and ISO 965-3 with thread angle 60o.
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