Sealey-Reverse-Action-Spark-Plug-Thread-Chasers-Sealey-MS003-p-Specially-designed-to-repair-damaged-spark-plug-threads-on-modern-engines-Unique-design-allows-the-tool-to-be-passed-through-the-plug-thread-into-the-combustion-chamber-then-expanded-to-the-correct-size-starting-on-the-inner-undamaged-threads-Traditional-thread-restorers-rely-on-luck-for-the-restored-&-undamaged-threads-to-align-The-first-letter-s-of-a-Denso-NGK-&-Bosch-plug-code-is-the-thread-size-identification-For