NGK Iridium IX Spark Plug vs DENSO Iridium Power IK20 Spark Plug

The NGK Iridium IX (LFR6AIX-11) and DENSO Iridium Power IK20 are both iridium-tipped plugs with 14 mm threads, 5/8 hex and a 5,000 ohm resistor, but they are not interchangeable: the NGK has a 26.5 mm reach and the DENSO a 19 mm reach, so the right one is set by your engine, not by preference. The DENSO uses a finer 0.4 mm iridium center electrode and a U-groove ground for a strong, consistent spark; the NGK uses a taper-cut ground and a solid non-removable terminal. Owners of both report long service life and steady idle, and neither brand has a clear durability edge when the correct plug is fitted. Buy the one your engine specifies.

• Choose the NGK Iridium IX if your engine calls for a 26.5 mm reach plug and a solid, non-removable terminal nut.
• Choose the DENSO Iridium Power if your engine calls for a 19 mm reach plug and you want the finer 0.4 mm iridium electrode with a pre-set 1.1 mm gap.