Upgrade your Ford Mustang, Capri, Thunderbird LTD 3.8 with these high-quality spark plugs from Autolite. Made from durable copper material, these vintage spark plugs have a thread diameter of 14mm and a hex size of 5/8 inches. They fit perfectly with a standard configuration and are compatible with gasoline fuel type. The package includes 6 spark plugs with a voltage of 12V and an installation depth of 17.5mm. These spark plugs are compatible with various part numbers including RS14YC, RS12YC, R44LTS, 408, and 408CC. They are OE/OEM part number SP427 and are made in the United States. Improve your car's performance with these spark plugs from Autolite.