the iridium alloy is used because of its durability and reliability. on an average plug, a narrow core typically shortens life span of plug but with the intense durability of iridium there is no sacrifice in any longevity. with a high melting point of 2454 degrees c, opposed to the 1769 degrees c of white gold, the electrode can tolerate the high levels of compression and minor knocking without any deterioration. a nickel coating on the housing also prevents the spark plug from premature deterioration. the iridium plugs are available for multiple applications and offered in colder heat ranges of 7 and up and specifically for rotary, heat ranges of 9 and up are offered. plugs priced each. most applications in stock