This set of 4 Splitfire SF40D spark plugs is perfect for anyone looking to replace their old or worn out spark plugs. Made of high-quality copper and with a thread diameter of 14mm, these vintage spark plugs are suitable for gas-powered vehicles with a 12V voltage. These spark plugs are compatible with a variety of different part numbers, including 104, 404, RN4C, AGS4CF4, W20ESR-U, and OE/OEM part number 5569737. With a hex size of 13/16in and an installation depth of .75in, these spark plugs are standard configuration and will fit perfectly into your ignition system. Upgrade your vehicle's performance today with these Splitfire spark plugs.