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NGK 3521 Spark Plug
| Brand | NGK 3521 |
|---|---|
| Resistance | 5000 |
| Ground Electrode Tip Design | Taper cut |
| Ground Configuration | Standard |
| Ground Electrode Core Material | Nickel |
| Electrical Terminal Type | Removable nut |
| Center Electrode Core Material | Copper |
| Center Electrode Tip Material | Iridium |
| Pre-Gap Size | .032 |
| Ground Electrode Quantity | 1 |
| Hex Size | 5/8 |
| Insulator Height | 50.00 |
| Manufacturer Heat Range | 9 |
| Seat Type | Flat |
| Reach | .75 |
| Thread Diameter | 10.00 |
| Part Number | Cr9eix |
| Stock Number | 3521 |
| Fits | — |
Iridium tip. Provides strong spark performance and long service life.
Taper-cut electrode. Promotes efficient ignition for consistent combustion.
OE legacy. Built by a leading spark plug supplier with decades of automotive expertise.
Cross-references AMS Automotive 4132, AMS Automotive 4191 and Anchor 3521 for the same application. See all 20.
NGK Iridium IX CR9EIX Spark Plug
NGK Iridium IX spark plug part number 3521 is built for precise ignition performance in applications that call for a 10 mm, flat-seat plug with a .75 reach and 5/8 hex. It uses an iridium center electrode tip, a copper core center electrode, and a nickel ground electrode to support consistent spark delivery and stable combustion.
Key Features
- NGK Iridium IX spark plug, part number 3521
- Iridium center electrode tip with copper core center electrode
- Nickel ground electrode with taper-cut tip design
- 5000 ohm resistance for ignition system compatibility
- Pre-gapped to .032
- Flat seat, 10.00 mm thread diameter, .75 reach, 5/8 hex
- Heat range 9 for specified engine applications
- Removable nut terminal
Product Details
The NGK Iridium IX line is engineered for drivers who need a spark plug that matches OE-style dimensions and ignition requirements while using iridium at the firing tip for durability and consistent spark characteristics. Part number 3521, also identified as CR9EIX, is a direct-spec plug for engines that require this exact thread size, reach, seat type, and heat range. It is a practical choice for motorcycle and small-engine applications, and it is also referenced in cross-application catalogs for select Honda Civic and Acura Integra listings where the same plug specification is called for.
This part cross-references Monroe Shocks & Struts (e.g., 5633) for the same application.
Common Issues This Plug Can Address
- Hard starting caused by worn or fouled spark plugs
- Rough idle from inconsistent ignition output
- Misfire conditions related to degraded plug electrodes
- Reduced throttle response from weak spark delivery
- Maintenance replacement for engines specified to use CR9EIX / 3521
Installation Notes and Tips
Verify the engine calls for a 10 mm, flat-seat spark plug with a .75 reach and heat range 9 before installation. Check the gap against the engine specification, confirm terminal style requirements, and inspect the ignition coil or plug wire condition at the same time. For fitment-based searches, this plug is commonly referenced for Honda Civic and Acura Integra applications where the CR9EIX specification is required.
Quality Assurance
NGK is a long-established OE supplier with broad coverage across automotive, motorcycle, marine, and small-engine applications. The brand’s manufacturing focus on original-equipment standards supports consistent fit, durability, and ignition performance for specified applications.
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|---|---|---|---|---|
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