Understanding Denso Spark Plug Numbering System
Understanding the Denso Spark Plug Number System: A Complete Guide for Australian Drivers
When you’re replacing spark plugs—whether for a daily driver, performance build, or small engine—choosing the correct plug is essential. Denso, one of the world’s most trusted ignition component manufacturers, uses a detailed numbering system to identify each plug’s specifications.
If you’ve ever wondered what all those letters and numbers mean, this guide breaks it down clearly.
Why the Spark Plug Code Matters
Every engine requires a specific spark plug design to deliver the right heat range, firing performance, and fit.
The Denso code on each plug helps you identify:
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Thread size
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Hex size
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Reach (thread length)
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Heat range
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Firing end design (resistor, iridium, platinum, etc.)
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Special design features
Understanding the Denso numbering system ensures you choose the right plug for your engine—preventing misfires, poor fuel economy, and potential damage.
How the Denso Spark Plug Code Works
A typical Denso spark plug code may look like this:
IK20TT
K16R-U11
SK20R11
Each part of the code represents a different specification.
Below is a breakdown of the primary components:
1. Thread Diameter & Construction (First Letters)
The first one or two letters represent the thread size and thread reach.
Examples:
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I – Iridium
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K – 14 mm thread, 19 mm reach
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U – 14 mm thread, 19 mm reach (older type)
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S – 14 mm thread, 19 mm reach, fine-wire platinum
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X – 10 mm thread
These letters instantly tell you the physical size and type of the plug.
2. Heat Range (First Number)
Denso heat ranges use lower numbers for hotter plugs and higher numbers for colder plugs.
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Typical range: 14–24
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Example:
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K16R-U11 → Heat range 16 (standard hot)
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IK20 → Heat range 20 (colder, performance-oriented)
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Colder plugs dissipate heat faster and are used in turbocharged or high-performance engines.
3. Thread Reach & Special Features (Middle Letters)
After the heat range, additional letters describe firing-end design.
Examples:
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R – Resistor
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P – Projected tip
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TT – Twin Tip (Denso’s modern fine-wire twin electrode design)
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U – U-groove
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E – 19 mm reach
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L – Long reach projection
These letters indicate how the spark plug behaves under combustion and how it fits in the cylinder head.
4. Gap Size (Final Numbers)
Many Denso plugs end with a gap number, where:
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11 = 1.1 mm gap
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9 = 0.9 mm gap
Example:
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K16R-U11 → Pre-gapped to 1.1mm
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SK20R11 → Fine-wire platinum, 1.1 mm gap
Most modern plugs are pre-gapped from factory, but always check manufacturer specs before installation.
Example Code Breakdown
IK20TT
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I – Iridium
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K – 14 mm thread, 19 mm reach
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20 – Cold heat range
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TT – Twin-Tip technology
Use: Performance cars, turbo engines
K16R-U11
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K – 14 mm thread
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16 – Standard heat range
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R – Resistor
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U – U-groove
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11 – 1.1 mm gap
Use: Common across older Toyota, Mitsubishi, Nissan engines
SK20R11
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S – Fine-wire platinum
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K – 14 mm thread
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20 – Cold heat range
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R – Resistor
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11 – 1.1 mm gap
Use: High-efficiency late-model engines
How to Choose the Right Denso Spark Plug
To select the correct plug:
1. Check your vehicle’s OEM recommendation
Every engine has a specific heat range, thread size, and plug type.
2. Match the Denso code to the specification
Iridium and TT series are great upgrades for longevity and performance.
3. Avoid changing heat range unless required
Performance engines may require a colder plug, but daily drivers should stick to OEM heat range.
4. Buy from reputable suppliers
To avoid counterfeits, always purchase from trusted automotive parts warehouses.
Denso Spark Plugs at King Parts Warehouse (Chirnside Park, Melbourne)
If you need the right Denso spark plug for your car, King Parts Warehouse stocks spark plugs to suit older Toyota, Ford, Holden, Nissan, Mazda, Mitsubishi, Subaru and more.
Whether you’re a DIY mechanic or running a workshop, we deliver Australia-wide with fast dispatch from Melbourne.