Magnetic plugs are a small investment that can help to prevent damage and wear in engines and gearboxes. They provide an easy way to check for unusual wear which may precede a failure. Small ferrous (iron / steel) particles in your oil or coolant stick to the magnet for inspection. This also helps to minimize further damage that these abrasive particles can cause when they are allowed to circulate.
Use this plug to replace any standard 1" NPT drain plug in your oil tank, cooling system, or transmission.