What is the difference mechanically from using an iridium tipped plug versus a non iridium tip?
The spark plug gap on a spark plug is where the spark jump across the electrodes. The spark will melt the metal electrodes part of the spark plug where the spark jumps. When copper is used on the electrodes the spark will melt parts over about 30,000 miles before they will need to be changed again. If Iridium is used the precious metal is harder than copper and will withstand the high temperature of the spark on the electrodes. They will wear at a much slower rate and will last over 100,000 miles with little to no wear.