Denso Iridium Long-Life Spark Plugs 3421 — 8-Pack .043" (1.1mm) Gap, Iridium Core for Reliable Ignition

These are genuine Denso Iridium long-life spark plugs (model 3421), sold as an 8-piece set with a .043" (1.1 mm) electrode gap for direct replacement in compatible engines.

If you need reliable ignition components for a maintenance job or tune-up, this boxed set of eight Denso 3421 spark plugs provides factory-quality parts and original packaging. Denso is an established OEM supplier, and the iridium-tipped electrodes in this model are engineered to deliver consistent spark performance and extended service life compared with standard copper plugs. This product listing covers the authentic Denso parts, shipped as a complete eight-plug pack intended to replace worn or failing plugs in vehicles that call for this specific part number and gap size.

How do these Denso iridium plugs improve ignition consistency?

The iridium center electrode offers a finer tip and higher melting point than conventional materials, which helps maintain a focused, steady spark over long service intervals. That focused spark enhances combustion stability under varying driving conditions without changing engine systems.

• Iridium core center electrode for reliable spark delivery
• Fine tip design promotes efficient combustion
• Durable construction resists wear and maintains gap
• Sold as a matched set of eight for uniform replacement

Will these plugs fit my vehicle and how do I confirm compatibility?

These are Denso part number 3421 with a .043" (1.1 mm) factory gap; compatibility depends on your engine’s specified plug type and heat range. Always verify fitment against your vehicle’s service manual or the retailer’s confirmed-fit tool before purchase to ensure correct thread size, reach, and heat rating.

• Part: Denso 3421, gap set to .043" (1.1 mm)
• Confirm thread size and reach with vehicle specifications
• Use seller/retailer fitment tools or OEM cross-reference lists
• Replacement requires same heat range and seat type as original

How should I install and maintain these spark plugs for best results?

Install by hand-first threading to avoid cross-threading, then torque to the manufacturer’s specification using a torque wrench or a calibrated socket. Check and re-torque if the engine head is aluminum and follow routine inspection intervals to maintain optimal gap and performance.

• Hand-thread before final torque to prevent damage
• Apply recommended torque from vehicle manufacturer
• Inspect gap and electrode condition at service intervals
• Replace in matched sets when multiple plugs are fouled or aged

What’s included in the box and why buy the 8-pack?

This listing includes eight genuine Denso 3421 spark plugs, original packaging, and any small hardware packaged by the manufacturer. Purchasing the full set ensures all cylinders receive identical, factory-matched plugs—important for balanced engine performance and smoother operation.

• Eight genuine Denso 3421 spark plugs in original packaging
• Includes manufacturer hardware where applicable
• Sold as direct-replacement components—no modification needed
• Convenient for multi-cylinder engines and full-tune-up jobs

Who is this for: Mechanics, DIY enthusiasts, and fleet owners looking for OEM-quality ignition components will find this set suitable when the vehicle manufacturer specifies Denso 3421 or an equivalent iridium plug with a .043" (1.1 mm) gap. Choose this eight-pack when you need consistent, long-life spark plugs for a complete tune-up of multi-cylinder engines and want the reassurance of authentic Denso parts.