Our Cross-Reference Methodology

We use several methods to identify interchangeable spark plugs. Each method is presented in its own section on the spark plug page.

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Note: Cross-references are for informational purposes only. Always verify fitment before purchase—even manufacturers recommend it.

Cross-reference

These references come directly from official documents and tools provided by manufacturers.

Autolite cross-reference PDF

Denso Cross-Reference Tool

Deep reference

This section builds upon basic cross-references by adding another layer of equivalence.

For example, if NGK X = Denso Y, and Denso Y = Bosch Z, then we can infer NGK X = Bosch Z.

We call this Deep Reference — an extended cross-reference using the chain of verified equivalencies.

Same specs

This section includes spark plugs that are fully interchangeable based on matching technical specifications. All listed plugs must have identical attributes:

Thread Size
Thread Pitch (Thread Spacing)
NGK Heat Range*
Hex Size (mm)
Gap Size (mm)
Seat Style (Seat Type)
Ground Electrode Type
Resistor (Ohms)
Projected Electrode Design (Yes/no)

NGK Heat Range*

Because manufacturers use different heat range scales, we normalize all values to NGK's range. The table below maps equivalent heat ranges across brands:

NGK	Bosch	Denso	Champion
2	10	9	18, 19
4	9	14	14, 16
5	8	16	11, 12
6	7, 6	20	9, 10
7	5	22	7, 8
8	4	24	6, 61, 63
9	3	27	4, 59
9.5	—	29	57
10	2	31	55
10.5	—	32	53
11	—	34	—
11.5	—	35	—
12	—	37	—

Note: Brands not listed in the table do not have a consistent mapping to NGK heat ranges and are therefore excluded from this section.

Bigger gap

Spark plugs listed here match all other specifications, but have a slightly larger gap—typically +0.1 mm to +0.3 mm.

While OEM gap sizes are recommended, a slightly larger gap can improve combustion by creating a bigger spark, which leads to a faster burn.

This method is useful when dealing with modern spark plugs that can't be regapped due to their materials or construction.

One step colder

These spark plugs match all required specs but have a heat range one step colder according to the NGK heat scale.

One-step colder plugs are ideal for modified engines with a 75–100 HP increase or for high-performance conditions like track driving. They help manage extra heat generated under such conditions.

Two steps colder

Spark plugs in this category are two steps colder (per NGK heat range) while matching all other critical specifications.

They are typically used in heavily modified engines with power increases of 150–200 HP, helping to prevent detonation and maintain optimal engine performance under extreme conditions.