The Lisle Inline Spark Tester W/ Coil On Plug Wire - 20580 is a diagnostic tool used to test the spark plug wire and ignition coil on vehicles with coil-on-plug ignition systems. It features an easy-to-read LED display, a spark gap indicator, and a durable construction for long-term use. It is designed to quickly and accurately diagnose problems with spark plug wires and coils, providing reliable results for automotive repair professionals.