Autolite Xtreme Start Iridium Lawn & Garden Spark Plug Automotive Replacement, XST458DP

What It Is

The Autolite Xtreme Start Iridium Lawn & Garden Spark Plug (XST458DP) is a high-performance replacement plug designed for 4-stroke lawn mowers, tractors, zero-turn mowers, and other outdoor power equipment. It uses an iridium fine-wire center electrode for easier starts and longer service life compared to standard copper plugs.

Fitment & Compatibility

Before buying, confirm this plug matches your engine’s required heat range, thread size (14mm), reach (0.708 inch), and gap (pre-set at 0.030 inch). Check your owner’s manual or current plug number for a cross-reference—this replaces common OEM numbers like Champion RC12YC, NGK BPR5ES, or Autolite 3924. It fits most Briggs & Stratton, Kohler, Kawasaki, Honda, and Tecumseh engines used in push mowers, riding mowers, and generators. Do not rely on deck size alone; always verify engine make and model.

Key Things to Know

• Installation is simple – No special tools needed; just a spark plug socket and torque wrench (recommended: 20-30 ft-lbs). Avoid over-tightening.
• Iridium lasts longer – Expect 25,000+ miles or several seasons in normal use, far outlasting copper plugs.
• Pre-gapped, but double-check – Factory gap is 0.030 inch, but shipping can knock it off. Verify with a gap tool before installing.
• Not for 2-stroke engines – Designed exclusively for 4-stroke lawn and garden equipment. Using in a 2-stroke will cause misfire and damage.

Should You Buy It

If you want a reliable, long-lasting spark plug that improves cold starts and resists fouling in modern engines, this is a solid upgrade over standard copper plugs. It’s ideal for anyone who mows frequently or wants to reduce maintenance intervals. Avoid it if your engine requires a different heat range or reach—check fitment first.