APR Iridium Pro Spark Plugs 14x19x16mm Heat Range 9 SingleAPR Iridium Pro Spark Plugs are the excellent upgrade for tuned engines. Our spark plugs are made from Iridium, which is one of the strongest materials you can use in this type of application. They run cooler, resist preignition, last longer than other materials with higher melting points, and even require less voltage to produce a strong spark. The electrode is harder and stronger than other materials, can dissipate heat more easily, is better