Iridium XP Spark Plug Autolite XP5144 Autolite Iridium XP spark plugs are engineered with an iridium-enhanced fine-wire and a proprietary, platinum ground electrode, to increase durability*, while its tapered ground wire maximizes engine efficiency, delivering improved engine performance, fuel efficiency, acceleration, and ignitability. Designed with a nickel-plated shell that is corrosion resistant to provide increased durability for extended periods. Includes a lifetime limited warranty that guarantees optimum performance equal to OE designed plugs. Engineered with an Iridium-enhanced center electrode and fine-wire design that increases ignitability and provides a more focused ignition for improved engine performance. Its proprietary platinum ground electrode provides increased durability* and resistance to wear, extending the life of the plug. The tapered ground wire improves engine ignitability. Its high alumina multi-rib ceramic insulator provides thermal conductivity and superior insulation for increased strength while preventing flash-over. Center Electrode Design: Machined Fine Wire Center Electrode Tip Material (Inch): Iridium Ground Electrode Tip Design: Tapered Ground Electrode Tip Material: Platinum Hex Size (Inch) : 5/8 Thread Diameter (Millimeter): 14 Reach (Inch): 0.809 Seat Type: Tapered Pre-Gap Size (Inch): 0.054 Manufacturer Heat Range: 9 Resistance (Ohm): 4000 Center Electrode Projection: Long Projection Terminal Type: Non Removable Nut