Autolite AP5325 Platinum Spark Plug, Pack of 1 Full platinum tip ensures virtually no gap erosion for long plug life. Hex Size: 5/8 inch Yttrium enhanced, high nickel alloy side electrode maintains precise gap to increase plug life Necked-down center electrode fires quicker and cleaner, with less voltage for easier starts, quicker acceleration, and improved fuel economy Platinum alloy pad on ground electrode provides extended durability and service life and platinum-to-platinum firing Nickel-plated steel shell for long-life corrosion resistance