This set of spark plugs is a great addition to your engine. With a thread diameter of 14 mm and a hex size of 21 mm, they fit standard configurations and are compatible with gasoline fuel type. These vintage Splitfire spark plugs, with manufacturer part number SF8G6, have a voltage of 12 V and are made of copper material. They have interchangeable part numbers of 66, 847, and RJ18YC6, and OE/OEM part numbers of 5613882 and 5613564. Made in the United States, they are performance parts that are suitable for a range of cars and trucks. Upgrade your ignition system with this high-quality set of spark plugs.