I have a set of these aswell, Denso Iridium Plugs IK24's,
DENSO’s patented iridium alloy is extremely tough and wear-resistant. This makes it possible to produce a spark plug with a centre electrode of just 0.4 mm. Denso Iridium spark plugs give a stronger spark and better ignition performance in all areas of driving. These plugs can withstand even the most severe conditions and have proven themselves in original equipment and racing. This product gives DENSO the leading position in Iridium Spark Plug technology.
but found the NGK's where better, smoother, more mpg, quiter tickover! All with just a change of sparkplugs