yes, the denso iridium's at $12/plug have the 0.4mm center iridium electrode. The electrode is finer ( thinner or sharper ) than the ngk's at 0.6mm or 0.7mm. The thinner and sharper you can make the electrode (where spark comes from), the easier it is for the spark to jump the gap and the lower the voltage needed for there to be a spark. End result "should" be better performance. That is why you pay more for the denso 0.4mm than the ngk's.
You do not gap any iridium plug as far as I am aware of. At most, you can only close the gap if the particular plug has a 0.050-0.060" gap and your car is old with an older ignition system which specs 0.030"-0.040" spark plug gap. The iridium plugs, which are also called "fine wire electrode" spark plugs, can inherently run larger gaps because the electrode is so thin and easier for the spark to happen.
Iridium's are advertised to last longer than platinum spark plugs, so you should not have to replace them at "standard" intervals. At $8+ a plug, I certainly wouldn't. You should get 30k-50k without question. The biggest problem is the plug threads seizing in the cylinder head if left in there for 6 years or 100k miles and anti-sieze lube isn't used. The shell and threads are no different and can rust.
My best guess is because iridiums are designed to fire easier, it would help out in an application that had a weak coil. But at $8-12/plug, that's about $50 and only band-aiding the problem. Not the best way to go, probably better spending the money on a new coil and ensuring the ignition is %100. If it isn't, then plugs become a waste if they're not getting good spark in the first place.
There's a lot of hoopla on the web about copper plugs being the best for heat dissipation and preventing detonation, and how copper is "a better conductor". Most of it is misinformation and info taken out of context. Some brand of plugs may run better is certain engines, but fact is the 2 requirements are the correct spark plug reach into the cylinder and the correct heat range plug. Some plugs may have different electode and ground strap designs, which will certainly influence performance especially if the tip is projected versus one that isn't. As for platinum's (or iridiums) being more likely to cause detonation because they don't dissipate heat as good as the metal copper, that's misinformation. If your platinum/iridium is too hot and causing detonation, then you need a colder plug simple as that. And conductivity is irrelevant as well, people see 10-6 vs 10-8 ohms and think that means something. It doesn't. Air/fuel ratio, heat, gasoline quality are factors that are orders of magnitude bigger in influence. That would be like saying my car is faster in the morning because it's before I eat breakfast/lunch/dinner, or after I take a dump, and the car is 0.5 pounds lighter.
