Iridium spark plugs - NGK's premium spark plug benefits from the addition of the precious metal 'Iridium' in it's construction. Harder than other precious metals used in spark plugs and with an extremely high melting point; allow for an even smaller diameter centre electrode to be manufactured (0.6mm) without compromising it's durability/service life. This extremely small iridium tipped electrode concentrates the available electrical energy which combined with the taper cut ground electrode design ensures this plug has superior gas flow qualities and lower voltage requirements, in turn offering improved performance in starting, idling and most importantly throttle response!