Denso SK20HR11 Iridium Platinum Spark Plugs 4-Pack (3421) — OEM Fit, Long-Life Ignition

DENSO SK20HR11 (3421) iridium platinum spark plugs — genuine 4-pack designed for reliable ignition and long service life in compatible vehicles.

These are original Denso spark plugs (part number 3421) sold as a 4-piece set. The SK20HR11 construction combines an iridium center electrode with a platinum ground electrode to provide a fine spark gap, improved wear resistance, and consistent firing across a variety of gasoline engines. This listing includes free shipping within the USA and territories, and each order contains four spark plugs—ready to install as a full-set replacement.

What makes the SK20HR11 different from standard spark plugs?

The SK20HR11 uses premium metals and a refined tip geometry that help maintain a stable spark over time. Iridium and platinum electrodes resist erosion better than conventional materials, preserving gap integrity and ignition consistency under normal driving conditions.

• Iridium center electrode for a smaller, more focused spark area
• Platinum ground electrode to slow wear at the firing edge
• Manufactured to Denso OEM tolerances for fit and function

How do these plugs affect starting and throttle response?

Up-to-spec spark plugs can improve combustion stability, which often translates to more reliable cold starts and crisper throttle transitions. While behavior depends on the vehicle and condition of other systems, fresh plugs remove a common source of misfires and uneven idling.

• Cleaner spark reduces misfires and rough idle potential
• Consistent ignition can improve throttle smoothness
• Full 4-plug set restores uniform firing across cylinders

Which vehicles and situations are these Denso plugs intended for?

The SK20HR11 (3421) is designed to match applications specified by Denso and many OEMs where this engine heat range and thread size are required. They're best used as a like-for-like replacement or when upgrading worn standard plugs to iridium/platinum construction.

• Direct replacement where Denso 3421/SK20HR11 is listed
• Recommended when replacing a full set of engine plugs
• Appropriate for everyday driving and highway use when matched to vehicle specs

What comes in the box and what should I check before fitting?

This product ships as a sealed pack of four genuine Denso spark plugs labeled with part number 3421. Before installation, verify thread size, reach, and heat range against your vehicle’s service manual or parts guide to ensure compatibility.

• Includes four Denso SK20HR11 (3421) spark plugs per order
• Inspect thread and electrode condition; check OEM gap if needed
• Use correct torque and anti-seize/coil-specified procedures during installation

Who is this for: This 4-pack is intended for vehicle owners, independent mechanics, and service shops seeking genuine Denso replacement plugs in the SK20HR11 (3421) specification. Choose this set if your vehicle’s maintenance schedule calls for these part numbers or if you want an OEM-grade iridium/platinum option for improved durability and consistent ignition. Free shipping within the USA and territories makes it convenient for anyone replacing all four plugs at once.