HIGH QUALITY MATERIAL: The spark plug tester is made of high quality plastic + metal, which is durable. Not easy to age, with good toughness, hardness and balanced mechanical properties, low impact resistance and high quality products. The flexible double ended tool with internal bulb lasts for years and is replaceable thanks to the transparent housing. . Easy to use: just connect the metal end of the tester to the spark plug coil and start the engine. If the ignition cable is intact, the indicator lamp lights up. Use this spark tester to check the health of each cylinder's ignition system without expensive mechanical maintenance. . Easy to Observe: The transparent observation window makes it easy to observe the rollover situation and confirm whether it is normal and easy to operate. Simply connect the tester between the spark plug and the spark plug wire and when a spark is sent, the tester will reflect the spark and ignite it. Look for dirty spark plugs, broken spots. It seems clear at first glance . Wide range of applications: The engine coil tester is essential for troubleshooting all internal and external combustion engines, such as cars, trucks, motorcycles, lawn mowers, chainsaws, snow cutters, snow blowers, generators, etc. Don't miss it .