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Keep Ignition Consistent Under Heat and Cylinder Pressure
Correct plug dimensions and heat range are essential to reliable ignition and safe engine operation. NGK 6668 is built for automotive engines that specify the plug dimensions and heat range shown in the Fitment table. Key details are box of four NGK LFR6A spark plugs and v-Power nickel center electrode with V-groove design.
Key Features
- Box of four NGK LFR6A spark plugs
- V-Power nickel center electrode with V-groove design
- Copper-core construction
- Resistor spark plug with 5,000-ohm resistance
- M14-1.25 thread
- 26.5 mm reach and 16 mm hex
- Gasket seat
- 0.9 mm preset gap
- NGK heat range 6
- Fixed SAE terminal
Fitment
No year-make-model fitment applies. Confirm every dimension, interface, clearance, load, and installation requirement shown below.
| Application Type | Requirements |
|---|---|
| Dimension Based | Automotive replacement use only where the vehicle or engine manufacturer specifies NGK LFR6A; verify M14-1.25 thread, 26.5 mm reach, 16 mm hex, gasket seat, 0.9 mm gap, and heat range 6. No year-make-model fitment is claimed. Motorcycle, ATV, powersports, personal-watercraft, and marine applications are excluded from this listing. |
Specifications
| Detail | Value |
|---|---|
| Brand | NGK |
| Manufacturer Part Number | 6668 |
| Product Type | Spark Plugs |
| Service Number | LFR6A |
| Construction | Nickel V-groove center electrode over copper core |
| Thread | M14-1.25 |
| Reach | 26.5 mm |
| Hex | 16 mm |
| Seat | Gasket |
| Gap | 0.9 mm |
| Heat Range | 6 |
| Resistance | 5,000 ohms |
| Ground Electrodes | 1 |
| Terminal | Fixed SAE |
| Quantity | 4 |
What's Included
- Four NGK LFR6A V-Power spark plugs
- Not included: Applications that do not specify the exact LFR6A plug
- Not included: Motorcycle, ATV, powersports, personal-watercraft, and marine applications
About NGK
NGK develops spark plugs and ignition components for OE and service applications, using defined heat ranges, electrode designs, and dimensions for exact engine fitment.
Related Parts
- Inspect application-matched ignition coils, wires or boots, and service tools before replacing the spark plugs.
FAQ
What is the 6668?It is a NGK spark plugs for automotive engines that specify the plug dimensions and heat range shown in the Fitment table, built around Box of four NGK LFR6A spark plugs.
What is the main benefit of this part?Box of four NGK LFR6A spark plugs; V-Power nickel center electrode with V-groove design.
Which applications does it fit?It is intended for automotive engines that specify the plug dimensions and heat range shown in the Fitment table. Use the Fitment table and every listed qualifier before ordering.
What comes with this product?Four NGK LFR6A V-Power spark plugs.
What construction details should I know?Nickel V-groove center electrode over copper core; 1.
What should be checked before installation?Compare the old and new parts, confirm position and orientation, and verify all application notes, clearances, fasteners, and required companion parts.
How should this part be installed?Confirm the engine manufacturer specifies the exact LFR6A plug and verify every listed dimension before removing the existing plugs. Follow all torque, alignment, bleeding, calibration, or break-in procedures that apply.
What warranty applies?Use the current NGK warranty terms supplied through an authorized retailer.
Installation Instructions
- Confirm the engine manufacturer specifies the exact LFR6A plug and verify every listed dimension before removing the existing plugs.
- Check the required vehicle or engine gap and inspect the new plugs without striking or bending the electrodes.
- Install into a cold engine by hand first to prevent cross-threading.
- Tighten to the vehicle or engine manufacturer's torque specification and verify normal operation.
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