Denso Iridium Long Life Spark Plugs Set — 8pc (3421) with 0.043" Pre-set Gap, Extended Life

These are genuine Denso Iridium Long Life spark plugs — an 8-piece set (model 3421) with a 0.043" (1.1 mm) pre-set gap and iridium-tipped electrodes for reliable ignition and extended service life.

If you need a complete replacement set for routine maintenance or a tune-up, this pack supplies eight factory-original Denso 3421 spark plugs. Each plug features an iridium core electrode designed to resist wear and maintain a stable spark over many miles. The set ships in original Denso packaging and includes the hardware required for straightforward installation; verify vehicle fitment using your dealer fit tool or Amazon’s Confirmed Fit before ordering.

How do Denso Iridium plugs improve ignition consistency?

Iridium-tipped electrodes use a harder, higher-melting-point metal than conventional plugs, which preserves the electrode shape and gap. That stability helps maintain a consistent spark pattern and can translate to smoother engine starts and steady combustion over time.

• Iridium core for reduced electrode erosion
• Stable 0.043" (1.1 mm) gap out of the box
• Precise manufacturing for uniform spark delivery

Are these plugs a direct fit for my vehicle?

Model 3421 is an OEM-style plug intended as a direct replacement for applications that specify Denso 3421. Compatibility depends on your engine’s required thread size, reach, and heat range, so always confirm fitment before purchase.

• Sold as an 8-piece genuine Denso set for multi-cylinder engines
• Check thread length and hex size against your vehicle specs
• Use online fitment tools or consult a parts dealer for verification

What should I expect during installation and routine maintenance?

Installation is the same as other threaded spark plugs: remove old plugs, inspect the threads and boots, and torque new plugs to the manufacturer’s specification. Because the gap is factory-set to 0.043" (1.1 mm), you typically won’t need to re-gap, though a quick check is recommended during service.

• Factory gap reduces initial setup time
• Follow vehicle torque specs to avoid thread damage
• Inspect ignition boots and wires or coils while replacing

How long can I expect these plugs to last compared with standard plugs?

Iridium electrodes are engineered for extended wear resistance, which commonly yields longer service intervals than conventional nickel plugs. Actual life varies by driving conditions, engine tune, and maintenance habits.

• Iridium construction for prolonged electrode life
• Consistent performance under typical driving loads
• Monitor for misfires, rough idle, or increased fuel use as replacement triggers

Who is this for: This 8-piece Denso 3421 Iridium Long Life spark plug set is geared toward DIYers, independent mechanics, and fleet technicians who need a full-kit replacement for eight-cylinder or multi-plug applications. It’s ideal when you want OEM-quality parts in original Denso packaging, a pre-set 0.043" (1.1 mm) gap to save setup time, and the longer-wearing characteristics of iridium electrodes. Confirm your vehicle’s required plug specification before purchasing to ensure correct fit and safe installation.